36 



U X I O . 



3 1 



OBLOXG. 



*Shuttleworthii. Lea. 



Demararaensis. 

 persulcatus. Lea. 

 *Yerreauxianus. Lea. 



SUBROTUND. 



*Newcombianus. Lea. 

 Unio sagrinatus. Sow. 



QUADRATE. 



*arc3eformis. Lea. Desk. Chenu. Han. 

 Unio nexus. 1 Say. 



Leibii. Lea. 

 *tesserula3. Lea. 



quadrans. Lea. 

 *Berlandierii. Lea. 



TRIANGULAR. 



*triangularis. Bar. Sh. & Eat. Hild. 

 Say. Han. 



TRIANGULAR. 



Unio formosus? Lea. (Male.) Chenu. 

 Unio cuneatus. Swain. 

 Mya triangularis. Eat. 



*Waccama\vensis. Lea. 



*Foremanianus. Lea. Chenu. 

 Unio velatus. Con. 



*"Woodwardianus. Lea. 

 *trinacrus. Lea. 

 *compactus. Lea. 



*elegans. 3 Lea. Chenu. Han. 

 Unio truncatus. Say. 



*donaciformis. 4 Lea. Desk. Chenu. 

 Han. 



*zigzag. Lea. Sh. & Eat. Desk. 

 Chenu. Han. 



*keterodon. s Lea. Con. Desh. Lins. 

 Han. 



*penitus. s Con. 



1 Say and Conrad both commit the error of giving precedence to nexus. My description of arcse- 

 formis is in my memoir, read before the American Philosophical Society, May 20, 1831, while Mr. Say's 

 was first described in the Transylvania Journal, of December, 1831. Subsequently, he republished it in 

 his American Conchology, No. 6, where he places erroneously the date of 1832 to my memoir. 



2 Mr. Barnes's description of triangularis was made from a female shell, and mine of formosus from 

 the male. There being an obvious distinction of the sexes in every specimen, my error was a very 

 natural one, as we were not at the time acquainted with the sexual differences in the Naiades. 



' Mr. Say thinks that Mr. Barnes's undulatus, Var. a, is the same with elegans. I think differently, 

 and would fortify my opinion in the fact that Mr. B. does not mention the zigzag rays which are strikingly 

 singular in the elegans, and could not have failed to elicit his remarks had it been under his eyes. 



* I have expressed my doubts, Transactions of the American Philosophical Society, vol. iv. p. 84 (p. 

 94 in " Observations on the Genus Unio," &c.), if this be more than a fine variety of zigzag (nobis). Mr. 

 Say gives it as a sj-nonym to nervosus, Raf., and Mr. Conrad as truncata, Raf. Prof. Kirtland thinks 

 this may be the female of zigzag. I am disposed to think that zigzag should be considered only a variety. 

 If the soft parts prove to be the same, then certainly zigzag is a variety of donaciformis. 



6 Mr. Conrad describes a Unio (Am. Jl. Sc., v. 21, Sec. Ser., p. 172) under the name of diver sus, 

 from Shoal Creek, North Alabama, which, he says, is remarkably like heterodon in form and teeth. 



* I received from Judge Tait, of Alabama, in 1830, several specimens of this species, but they were 

 not sufficiently perfect to induce me to publish them. Mr. Conrad does not mention the rays, a very 

 peculiar character of which is their being dotted somewhat like those of securis (nobis), but in a lighter 

 manner. 



