Dr. Rob Dillon, Coordinator





Monday, March 16, 2020

Is Marstonia ozarkensis extinct?

Editor’s Note – This is the second of a two-part series on an enigmatic hydrobiid with a last known address in northern Arkansas.  You really should go back and read my essay of 10Feb20 before proceeding through this month’s essay, if you haven’t already.

When last we left our fearless jpeg naturalist, he had just received several images of hydrobiid snails from Ms. Rachel Vinsel, the curatorial assistant at the Illinois Natural History Survey.  One image depicted cotypic Marstonia ozarkensis, collected by A. A. Hinkley in 1914 from the White River drainage in northern Arkansas [1], declared extinct by the US Fish & Wildlife Service in late 2018 [2].  That’s the first image in the photomontage below, reprinted from last month’s essay.

Ah, but there were “several images” attached to Rachel’s late February email.  She went on to add: 
“While I have you, I was wondering if you'd mind taking a look at image 0097 as well? This one was collected in the Kishwaukee River (Rock River Dr.) Winnebago Co., IL. It's not quite 3mm tall.” 
 Rachel’s image 0097 is labelled “Kishwaukee unknown,” second from left below:

All four approx 3 mm standard length
Holy crap, we have seen those little snails before.  At this point, could I ask you all to indulge me?  Would you mind opening up my essay of 19Jan16 in a new window?  Here’s the link:

In that charmingly-befuddled essay, you may remember my fumbling with a mysterious population of 3 mm hydrobiid snails collected from the muck of Lake St. Clair, 25 miles east of Detroit.  Check out the photos in that essay, one of which has been clipped and inserted third in the montage above.  And now could I ask you to refer to my follow-up essay of 5Feb16:

The matches between cotypic M. ozarkensis, Rachel’s Kishwaukee unknown and the Lake St Clair Marstonia letsoni is pretty darn near perfect, am I right?  And let me add yet another observation. 

In January of 2017 I was combing through a remarkable set of collections made by our good friend Ryan Evans up in Kentucky, when my eyes fell on a single, tiny shell from Elkhorn Creek, about 10 km north of Frankfort.  That shell is depicted at the far right of the montage above.  That’s pretty good match as well, am I right?

So we have now established two things.  In 2016, we demonstrated that populations of Marstonia letsoni are quite literally obscure – tiny snails, inhabiting dark recesses, sometimes in deep water.  To find one, you’d need to be more persistent or more lucky than I, your humble correspondent, who has never seen one in his entire 45-year career combing the lakes and rivers of America, overtly and deliberately committing premeditated acts of freshwater malacology in the first degree.

And we have now documented that Marstonia letsoni has a strikingly broad range.  Lake St Clair is 500 km north of Frankfort, KY, and 500 km east of the Kishwaukee River at Rockford, IL.  Could Marstonia letsoni range another 700 km to the Ozarks?  Might Marstonia ozarkensis (Hinkley 1915) be a junior synonym of Marstonia letsoni (Walker 1901)?

Let me make one final point in closing.  All authors who have any first-hand experience in this arcane little corner of malacology – Hinkley, Bob Hershler [3], and Shi-Kuei Wu [4] – have been unanimous that in overall morphology and life habit, both Marstonia ozarkensis and M. letsoni are very similar to a third species, Marstonia scalariformis.  The primary distinction is a carina or keel on the shell of scalariformis, which Wu and colleagues [4] observe “may be absent or only vaguely apparent” in some natural populations.  See Wu’s Figures 26 – 29 below.

M. ozarkensis (26, 27) and M. scalariformis (28, 29) from Wu [4].
Marstonia scalariformis rivals M. letsoni in both obscurity of life habit and vastness of range.  Wolf [5] described “Pyrgula” scalariformis in 1869 from a single shell found by the banks of the Illinois River.  Hinkley [6] described wabashensis from the Wabash River at the Illinois/Indiana border in 1908, which Hershler [3] synonymized under scalariformis in 1994, noting “variable carina development.”  Hershler’s figure of the penial morphology of scalariformis sampled from the Meramec River in Missouri shows bifurcation reminiscent of the letsoni penis figured by Berry [7].

And the “very incompletely known” range of scalariformis ranges all the way from central Illinois south down to tributaries of the Tennessee River in north Alabama [8].

Hinkley thought that the previously-described species most similar to his ozarkensis was wabashensis.   Hershler agreed, suggesting that wabashensis was a junior synonym of scalariformis and adding further that letsoni was also most similar to scalariformis, without directly comparing ozarkensis to letsoni.  I am not sure here today whether Marstonia ozarkensis (Hinkley 1915) is actually extinct, or if it was simply a local population of what has been called elsewhere letsoni (Walker 1901), or wabashensis (Hinkley 1908) or possibly even scalariformis (Wolf 1869), now here in the 21st century misunderstood into oblivion.


Notes:

[1] Hinkley, A.A. (1915) New Fresh-water Shells from the Ozark Mountains. Proceedings of the United States National Museum, 49:587-589.  This is actually the 1916 volume of the PUSNM, but Hinkley’s date of publication is given as “December 23, 1915” in the index.

[2] USFWS 2018.  Ozark snail species presumed extinct following science-based surveys.

[3] Hershler, R. (1994) A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae).  Smithsonian Contributions to Zoology 554: 1-115.

[4] Wu, S-K, R. D. Oesch & M. E. Gordon (1997) Missouri Aquatic Snails.  Missouri Department of Conservation, Jefferson City. 97 pp.

[5] Wolf, J.  (1869) Descriptions of three new species of shells.  American Journal of Conchology 5: 198.

[6] Hinkley, A. A. 1908. A new species of Pyrgulopsis. Nautilus 21: 117-118.

[7] Berry, E. G. (1943)  The Amnicolidae of Michigan: Distribution, ecology, and taxonomy.  Misc. Publ. Mus. Zool. Univ. Mich. 57: 1 – 68.

[8] Walker, B. 1906. New and Little Known Species of Amnicolidae. Nautilus, 19:114-117.  Walker identified the population collected by Mr. Hinkley near Florence, Alabama, as “Pyrgulopsis mississippiensis (Pilsbry),” which is a junior synonym of M. scalariformis, according to Hershler [3]. There are also museum records of M. scalariformis from the Flint River near Huntsville that need confirmation.


Monday, February 10, 2020

What was Marstonia ozarkensis?


All I know about the late Marstonia ozarkensis is what I’ve read in the newspapers.  The diminutive hydrobiid, small-bodied even by Marstonia standards, was originally described as “Pyrgulopsis ozarkensis” by A. A. Hinkley in 1915 [1] from the North Fork of the White River in north-central Arkansas, about 20 miles from the Missouri line.  Hinkley’s single-paragraph description focused entirely on the 3 mm shell (H, below), offering no anatomical observations on the animal itself, indeed no biological notes of any sort, beyond “found in shallow water on the bedrock.”

The taxon receded into utter obscurity (as opposed to mere obscurity) for 80 years, listed by Burch [2] but not figured.  Hershler [3] essentially reprinted Hinkley’s original description in his 1994 monograph with no additional observations, stating “A limited survey of this region in 1991 – 1992 did not yield this species.”  The scanning electron micrograph image of an ANSP paratype published by Hershler (a, below) was a poor likeness [4].

Marstonia ozarkensis: Hinkley [1], Hershler [3], INHS cotype.
In 1997 Wu and colleagues [5] reported the discovery of a population of P. ozarkensis in the North Fork of the White River in southern Missouri, about 45 km upstream from Hinkley’s type locality.  In 2002 Thompson & Hershler [6] resurrected the genus Marstonia and assigned Hinkley’s ozarkensis to it.  And in 2007 Christian & Hayes [7] reported a population of Marstonia ozarkensis in Mud Creek, a tributary of the Black River about 115 km east of Hinkley’s type locality.

Marstonia ozarkensis was one of the 404 “aquatic, riparian and wetland species from the Southeastern United States” listed in the megapetition filed by the Center for Biological Diversity in 2010 [8].  In response, the US Fish & Wildlife Service declared Marstonia ozarkensis “presumed extinct” in December of 2018 [9]

The authors of the FWS “Species Status Assessment” filed in August of 2018 [10] were unable to confirm the 1997 report of Wu and colleagues, finding that “the museum records cited for this population are not present in the museum database.”  And after some hemming and hawing about high levels of endemicity in North American hydrobioids, they concluded that the Mud Creek population “may be a morphologically similar undescribed species (D. Hayes, pers. comm.).”  Thus, to quote the 18Dec18 FWS press release [9] verbatim: 
Following rigorous, science-based surveys, the Ozark pyrg, a small snail native to Arkansas and Missouri, is presumed extinct, according to the U.S. Fish and Wildlife Service. No Ozark pyrgs have been confirmed in surveys since their first discovery in 1915. As a result of today’s finding, the pyrg will not be listed under the Endangered Species Act (ESA).
That sounds like the end of the story, doesn’t it?  For the Feds, it probably is.  But for us, not so much.

In late February of last year I was pleased to receive an email from Ms. Rachel Vinsel, the Manager for the Illinois Natural History Survey mollusk collection, with attached tif images of two hydrobiid shells collected in a wetland south of Chicago.  They were clearly Marstonia, but of what species?

I can boast of no special expertise in the hydrobioids, but I can picture-match with the best of ‘em.  So I pulled my trusty copy of Hershler (1994) out of the files and started thumbing through it, looking for clues to the identity of Rachel’s unknowns.  And my eyes were drawn to the poor likeness [4] of Marstonia ozarkensis reproduced at the top of this blog post.  Hershler’s figure looked like a possible match to the images Rachel had sent me.  And heck, it isn’t all that far from Chicago to Arkansas, is it?

But if I have learned anything from many years of misadventure as a jpeg naturalist, it is that there is no substitute for the actual specimens in hand.  And I happened to have a copy of the INHS freshwater gastropod holdings on my hard drive.  And I discovered that there are several lots of bona fide Marstonia ozarkensis in the INHS collection, collected by Hinkley himself in 1914.

So the next day I replied to Rachel, suggesting that her Chicago-area unknowns might represent a rediscovery of M. ozarkensis, but simultaneously emphasizing that she dig some of the bona fide M. ozarkensis out of the INHS collection and compare.  And on 25Feb19 she sent me a tif file depicting a really interesting series of little hydrobiids, featuring both her Chicago area unknowns and the INHS cotypic M. ozarkensis.

The “INHS” image at the far right of the photomontage that opened this essay was clipped from the photo Rachel sent me 25Feb19.  Three revelations struck me almost simultaneously.  First, and least importantly, Hershler’s figure, the only illustration I had seen to that point, didn’t look anything like bona fide M. ozarkensis.  Second, our Chicago-area unknowns didn’t look anything like bona fide M. ozarkensis either [11].  But thirdly and most importantly, the bona fide M. ozarkensis in the INHS did look a whole lot like something I had seen before.

And Rachel was not done.  There were additional tif files attached to her email of 25Feb19, including one that would challenge even that tiny little bit of knowledge I thought I might have been able to glean about the late Marstonia ozarkensis.  Tune in next time for, “Is Marstonia ozarkensis extinct?”


Notes

[1] Hinkley, A.A. (1915) New Fresh-water Shells from the Ozark Mountains. Proceedings of the United States National Museum, 49:587-589.  This is actually the 1916 volume of the PUSNM, but Hinkley’s date of publication is given as “December 23, 1915” in the index.

[2] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

[3] Hershler, R. (1994) A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae).  Smithsonian Contributions to Zoology 554: 1-115.

[4] Actually, to be fair.  It seems entirely possible to me that M. ozarkensis may have demonstrated a variety of shell form, to include the relatively robust form depicted by Hershler as well as the gracile depicted by Hinkley.  And possibly carinate forms as well, like Pyrgophorus or Potamopyrus?  Maybe even to the extreme of Marstonia scalariformis, perhaps?  But let's not get ahead of ourselves.

[5] Wu, S-K, R. D. Oesch & M. E. Gordon (1997) Missouri Aquatic Snails.  Missouri Department of Conservation, Jefferson City. 97 pp.

[6] Thompson, F. G. & R. Hershler (2002) Two genera of North American freshwater snails: Marstonia Baker, 1926, resurrected to generic status, and Floridobia, new genus (Prosobranchia: Hydrobiidae: Nymphophilinae).  The Veliger 45: 269 - 271.

[7] Christian A. D. & D. M. Hayes (2007) Diversity and distribution of freshwater gastropods from the Ozark region of Arkansas.  Report submitted to the Arkansas Game and Fish Commission.  34 pp.

[8] Center for Biological Diversity. 2010. Petition to list 404 aquatic, riparian and wetland species from the Southeastern United States as threatened or endangered under the Endangered Species Act.  For more, see:
  • Megapetitions of the Old West [14July09]
  • Megapetitions II: Armistice Day?  [18May11]
[9] The 12/2018 findings of the USFWS on Marstonia ozarkensis can be read here:
  • Federal Register: Endangered and threatened wildlife and plants; 12-month findings on petitions to list 13 species as endangered or threatened species [19Dec18]
  • Press Release: Ozark snail species presumed extinct following science-based surveys [18Dec18]
[10] U.S. Fish and Wildlife Service. 2018. Species status assessment report for the Ozark pyrg (Marstonia ozarkensis). 6Sept18. Atlanta, GA.  [pdf]

[11] Those two little shells of which Rachel initially sent me photos are not the subject of this essay.  I’m still not 100% sure what they were, but I think Rachel and I have settled on weirdly-fat and weirdly-dark Marstonia lustrica, and it doesn’t matter for our purposes here, anyway.

Tuesday, January 7, 2020

CPP Diary: The Many Faces of Professor Troost

Editor’s note: If you have not read last month’s post, read it.  And if you did read last month’s post, go back and read it again. The essay that follows was written under the assumption that the themes developed on 6Dec19 remain fresh in the minds of our readership.

Back in August we introduced the present “CPP Diary” series with an essay focusing on the Gap Creek populations of two freshwater gastropods widespread throughout the Tennessee/Cumberland [1].  In September and October, we explored the phenomenon of cryptic phenotypic plasticity (“CPP”) in one of those, Pleurocera simplex [2].  This month let’s back up and get a fresh start at that other species, shall we?

As I mentioned in August, the mission that sent me on my first visit to Gap Creek, way back in the summer of 2006, was a comprehensive VDGIF-funded survey of the pleurocerid fauna of SW Virginia.  John Robinson and I ultimately identified 83 populations of three species in our five-county study area, including 13 populations of what we were calling, at that time, “Goniobasis arachnoidea.”  We analyzed genetic polymorphism at 11 allozyme-encoding loci in 12 of our 83 populations, including three of the “arachnoidea,” reporting our results to the VDGIF in 2007 [3].

Almost all our Virginia populations of “arachnoidea” bore slender shells with small body whorls, usually striate, at least near the apex.  Shell (B) depicted second from left below, collected from Gap Creek at the TN 63 bridge, is typical.  But while genetically matching our other arachnoidea populations, the sample we analyzed from the headwaters of Gap Creek bore entirely smooth and strikingly stunted shells as shown at far left (A).  That population is so morphologically distinctive that it was described by Isaac Lea as not one but two unique species: Melania porrecta and M. vittatella [4].  This is an obvious example of CPP.

So to what population of snails, precisely, was the nomen “arachnoidea” originally intended to apply?  John G. Anthony [5] described his Melania arachnoidea in 1854 as “rather thin, spire slender and much elevated, very strongly striated and ribbed,” giving its type locality as “a small stream emptying into the Tennessee River near London, Tennessee.”  This must be a misspelling of Loudon, the town south of Knoxville, where the Tellico Dam [6] backs up the Little Tennessee River from its mouth to Chilhowee.  

I surveyed the precincts of Loudon in the summer of 2007 and happened to sample Steekee Creek at the bridge where it enters the corporate limits (35.7242, -84.3473) on its way to The Tennessee.  There I found, in addition to P. simplex and P. gabbiana, a population of pleurocerids bearing thin shells of slender spire and strong striation such as depicted in figure (C) below. 
(A) Gap Ck upstream, (B) Gap Ck downstream, (C) Steekee Ck, (D) Sycamore Ck

Goodrich [7] considered Lea’s (1862) Goniobasis spinella a subspecies of arachnoidea (Anthony 1854).  Lea [8] gave the type locality of spinella as “Sycamore, Claiborne County, Tennessee.  On maps of Claiborne county today one can find a wide place in the road marked “Sycamore Hall,” with a Little Sycamore Creek flowing freshly by just down the hill.  I collected specimen (D) depicted at far right above on May 14 of this year, from Little Sycamore Ck at the Estes Road bridge (36.4534, -83.5076).

But wait.  Before we plunge any further into the roaring 60’s, we really ought to paddle back about 20 years and pick up Isaac Lea’s (1841) Melania teres and M. strigosa [9].  The descriptions and figures of the two 1841 species were nearly identical to each other, as well as to arachnoidea of 1854 and spinella of 1862.  The shell of teres Lea observed was “remarkably elevated” with “spire drawn out” and “last whorl very small.”  The strigosa shell he also described as “spire drawn out,” remarking as he did that “This species is somewhat like teres herein described.”  Lea did mention “striate above” for strigosa, while not mentioning any shell ornamentation for teres.

The habitat Lea gave for Melania teres (Fig 27 way down below) was just “Tennessee Dr. Troost,” too vague to send us on a hunt today, although Goodrich [7] suggested “Small streams of Walden Ridge, Tennessee, flowing eastward.”  Figure 356 is scanned from Burch [10], presumably collected from one of those Walden Ridge teres populations illustrating Goodrich’s concept of the taxon.

For strigosa Lea did a bit better, “Tennessee Dr. Troost, Holston River Dr. Warder.”  This is probably John Aston Warder (1812 – 1883), who was born in Philadelphia and lived in Cincinnati, but traveled broadly [11].

The individual shell depicted in figure (E) down below was collected from Little Flat Creek at the Emory Road bridge in August of 2010 (36.1411, -83.7961). I am offering that particular population of pleurocerids bearing shells with spires drawn out, striate above, as topotypic for M. strigosa for four reasons.  First, apparently at least some of Lea’s sample(s) came from the Holston River drainage of Tennessee, somewhere.  And second, that entire drainage is a mess.

A=Gap up, B=Gap down, C=arachnoidea, D=spinella, E=strigosa, F=striatula, T=troostiana
In the last 10 – 12 years I have surveyed the pleurocerid fauna of the entire seven-county region drained by the Holston in East Tennessee, and have only discovered populations of pleurocerids bearing striate shells with spires-drawn-out in two streams: Mossy Creek in Jefferson County, about which you just read in my essay of 6Dec19 (Don’t tell me that you didn’t) and Little Flat Creek in Knox County.  Since Mossy Creek is already the type locality of M. troostiana, it seems an unlikely nominee for the type locality of M. strigosa.  That leaves Flat Creek as the sole remaining candidate.

The third reason I am offering Flat Creek as the type locality for M. strigosa is that it is in Knox County, and Goodrich [7] subsequently suggested the range of Goniobasis strigosa as “Small streams near Knoxville, Knox County, Tennessee.”  I’m not sure that amounts to a subsequent restriction of type locality, but I do very much value Goodrich’s opinions on matters of this sort.  And the fourth reason I am offering Flat Creek as the type locality for M. strigosa is simply that the shells of the population of pleurocerids living in that little brook match Lea’s figure.  They are not as strongly striate as the Mossy Creek sample that must have been in Isaac Lea’s collection since 1836.  They are merely “striate above.”  OK, good enough.

So what strikes me most about all these pleurocerid populations – much more than the shell striae – is the character that Lea called “spire drawn out” and that Anthony called “spire slender and much elevated.”  In more modern literature, this character is sometimes measured as shell length-to-width ratio, or the ratio of body whorl length to total shell length, although the statistical analysis of ratios is problematic.  In my own research I have preferred the regression of shell width on length [12], or the regression of apex height on body whorl height [13].  Regardless of what that variable is called, or how it is measured, the heritable component can be significant [14].

I am also stricken by the ecological similarities of all these populations.  All of these nominal species – arachnoidea, spinella, strigosa, and the Gap Creek populations that Lea described as porrecta/vittatella – reach maximum abundances in small, rich creeks.  They essentially disappear from the larger rivers of East Tennessee, not unlike Pleurocera simplex, at least in this part of the world.

Lea teres [9], Burch teres [10], Lea strigosa [9], Flat Ck (E), Coahulla Ck (F)
In exactly that same environment south of Knoxville Goodrich [7] identified populations of pleurocerids bearing striate shells with small body whorls as Goniobasis striatula (Lea 1841/43).  Lea [15] gave the habitat as just “Tennessee,” no help.  Most interestingly, however, Goodrich [16] also identified pleurocerid populations collected from Coahulla Creek in Whitfield County, Georgia, as G. striatula, shown in figure (F) at far right above.  This is one of the very few elements of the pleurocerid fauna that Goodrich admitted might be shared between Tennessee River drainages to the north and drainages of the Alabama/Coosa river system draining south toward the Gulf.

We have met the Coahulla Creek pleurocerid fauna before.  It was from Coahulla Creek in the NW corner of Georgia (34.9731, -84.9505) that I collected the sample of P. carinifera I analyzed in Dillon 2011, together with its control population of P. simplex [17].  The rivers and streams at the top of the Alabama/Coosa drainage are separated from drainages of the Tennessee by a couple kilometers at most.  And the genetic differences I found between Coahulla carinifera and simplex were not dramatically different from clavaeformis and simplex populations I sampled all the way through East Tennessee up into SW Virginia.

I did not gather any genetic data on P. striatula when I was sampling pleurocerids for my 2011 study.  But their similarities with Tennessee populations of arachnoidea, spinella, and strigosa in both ecology and shell morphology are striking, are they not?

All of the names given to all of the populations we have reviewed this month: porrecta (Lea 1863), vittatella (Lea 1863), arachnoidea (Anthony 1854), spinella (Lea 1862),  teres (Lea 1841), strigosa (Lea 1841), and striatula (Lea 1841) were proposed more recently than troostiana (Lea 1838).  And all are the same thing.  Populations of one single, highly variable species of pleurocerid snail, best identified as Pleurocera troostiana, extend down the length of the Tennessee River drainage, from SW Virginia through East Tennessee, and even hop the low hills to the upper Coosa drainage in NW Georgia.

Well, we’re not anywhere near done with the subject yet, but I sense that I’m about to lose my audience, all two of you, so let’s bookmark it here.

But our story will continue onward in future episodes, as does the river, downstream into North Alabama.  By the mid-nineteenth century, the fame of Isaac Lea seems to have spread throughout our entire, muscular young country.  And prominent citizens from Huntsville, Tuscumbia, and Florence, Alabama, were scooping up samples of the local gastropod fauna, drying them on their back porches, and packing them for Philadelphia, no different from the citizens of Knoxville and Nashville.

In our next installment... Huntsville hunt!


Notes:

[1] CPP Diary: Yankees at the Gap [4Aug19]

[2] Cryptic phenotypic plasticity in Pleurocera simplex:
  • CPP Diary: The spurious Lithasia of Caney Fork [4Sept19]
  • CPP Diary: What is Pleurocera ebenum? [3Oct19]
[3] Dillon, R. T. & J. D. Robinson (2007a) The Goniobasis ("Elimia") of southwest Virginia, I.  Population genetic survey.  Report to the Virginia Division of Game and Inland Fisheries.  25 pp.  [PDF]

[4] Lea, Isaac (1863) Descriptions of fourteen new species of Melanidae and one Paludina.  Proceedings of the Academy of Natural Sciences of Philadelphia 15: 154 – 156.

[5] Anthony, J.G. (1854) Descriptions of new fluviatile shells of the genus Melania Lam., from the western states of North America.  Annals of the Lyceum of Natural History of New York 6: 80 -132.

[6] This was the infamous “snail darter” dam, that led (perhaps more than any other public works project) to the crystallization of public antipathy for the impoundment of the free-flowing waters of the USA.  For more, see:
Wheeler, W.B. & M.J. McDonald (1986)  TVA and the Tellico Dam 1936 – 1979.  University of Tennessee Press, Knoxville.

[7] Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.

[8] Lea, Isaac (1862) Description of a new genus (Goniobasis) of the Family Melanidae and eighty-two new species. Proc. Acad. Nat. Sci., Phila., xiv, pp. 262-272.
Lea, Isaac (1863) New Melanidae of the United States.  Journal of the Academy of Natural Sciences of Philadelphia 5: 217 – 356.

[9] Lea, Isaac (1841) Proceedings o the American Philosophical Society 2: 11 – 15.
Lea, Isaac (1843)  Description of New Fresh Water and Land Shells.  Transactions of the American Philosophical Society 8: 163 – 250.

[10] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

[11] Wilson, JG & Fiske, J (1889) Appleton’s Cyclopaedia of American Biography Volume VI. Appleton, NY.

[12] Wethington, A.R., J. Wise, and R. T. Dillon (2009) Genetic and morphological characterization of the Physidae of South Carolina (Pulmonata: Basommatophora), with description of a new species.  The Nautilus 123: 282-292.  [PDF]

[13] Dillon, R. T. & J. D. Robinson (2016) The identity of the "fat simplex" population inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 16-18. [PDF]
Dillon, R. T. (2016)  Match of Pleurocera gabbiana (Lea, 1862) to populations cryptic under P. simplex (Say, 1825).  Ellipsaria 18(3): 10 - 12.  [PDF]  For more, see:
  • The Fat simplex of Maryville matches type [14Oct16]
  • One Goodrich Missed: The skinny simplex of Maryville is Pleurocera gabbiana [14Nov16]
[14] Dillon, R. T. & S. J. Jacquemin (2015)  The heritability of shell morphometrics in the freshwater pulmonate gastropod Physa.  PLoS ONE 10(4) e0121962. [html] [PDF]  For more, see:
  • The heritability of shell morphology in Physa h^2 = O.819! [15Apr15]
[15] This name is another cold mess.  Lea originally described it as “Melania striata” in that same pair of 1841/43 publications cited at [9] above.  He then discovered that the specific nomen striata was preoccupied, amending it to striatula elsewhere in 1843 (Proceedings of the American Philosophical Society 2:237).  Goodness gracious it will be nice to be done with stuff like this.

[16] Goodrich, C. (1941) Pleuroceridae of the small streams of the Alabama River system. Occas. Pprs. Mus. Zool. Univ. Mich., 427, 1-10.

[17] Dillon, R. T. (2011)  Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque 1818). Malacologia 53: 265-277 [PDF]. For more, see:
  • Mobile Basin III: Pleurocera puzzles [12Oct09]
  • Goodbye Goniobasis, Farewell Elimia [23Mar11]