754 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XXII. 



tPLEUROBEMA CURTA Lea. 



* Unio curtus LEA, Pr. Ac. N. Sci. Phila., Ill, 1859, p. 112; * Jl. Ac. N. Sci. Phila., 



V, 1862, p. 103, pi. xvn, fig. 253; *Obs., VIII, 1862, p. 107, pi. xvn, fig. 256. 

 * B. H. WRIGHT, Check List, 1888. 



* Mar gar on ( Unio) curtus LKA, Syn., 1870, p. 40. 



Toinbigbee River, Columbus, Mississippi. 



(Group of Pleurobema troscheliana.) 



Shell rather small, solid, rounded-triangular, inflated, somewhat 

 inequilateral, slightly pointed near the posterior base, and rounded 

 angular at the hinder end of the ligament; base of the shell almostevenly 

 rounded; posterior ridge low; beaks high and slightly curved inward 

 and forward over a well-defined lunule; epidermis dull tawny, showing 

 the rest periods and occasionally marked with a radiating row of dark 

 green, squarish spots in front of the posterior ridge; hinge plate wide 

 and flat; pseudocardiuals small, triangular, rough; laterals short, 

 curved; muscle scars small, rather deep. Animal with semicircular 

 gills, the inner the larger and free from the abdominal sac half to 

 nearly their whole length; ovisacs of outer gills apparently in pairs. 



tPLEUROBEMA TAITIANA Lea. 



*Unio (aitlanns LEA, Tr. Am. Phil. Soc., V. 1834, p. 39, pi. IV, fig. 11; *Obs., I, 

 1834, p. 151, pi. iv, fig. 11. *FERUSSAC, Guer. Mag., 1835, p. 29. *HANLKY, 

 Test. Moll., 1842, p. 186; *Biv. Shells, 1843, p. 186, pi. xxm, fig. 26. *CON- 

 RAD, Pr. Ac. Nat. Sci. Phila., VI, 1853, p. 258.- *H. and A. ADAMS, Gen. Rec. 

 Moll., II, 1857, p. 496. *T3. H. WRIGHT, Check List, 1888. * PJETEL, Conch. 

 Sam., Ill, 1890, p. 169. 



* Margarita ( Unio) taitianus LEA, Syn., 1836, p. 21; 1838, p. 18. 

 *Margaron (Unio} taitianus LEA, Syn., 1852, p. 25; 1870, p. 38. 



Alabama River. 



tPLEUROBEMA COR Conrad. 



* Unio'mytiUoides CONRAD, Am. Jl. Sci., XXV, 1834, p. 343. pi. I, fig. 7.' 



* Unio cor CONRAD, New F. W. Shells, 1834, p. 28, pi. in, fig. 3, p. 68.* FERUSSAC, 



Guerin Mag., 1835, p. 29.* M5LLER, Syn. Nov. Gen., 1836, p. 202. " HANLEY, 

 Test. Moll., 1842, p. 187; * Biv. Shells, 1843, p. 187.* CHENU, Bib. Conch., 1st 



1 Conrad says this is between Unio ellipsis Lea and mytilloides Rafinesque, but that 

 he has no doubt that it is the latter. It is certainly very different from the shell 

 Rafinesque figures and describes as Pleurobema mytilloides. (Ann. Gen. Sci. Phys. 

 Brux., XIII, 1820, p. 313, pi. LXXXII. figs. 8-10.) Conrad's Unio cor was published in 

 May, 1834, and his mytilloides in January of the same year, so that the latter has 

 priority, but as Rafinesqtie's name was placed under the genus Pleurobema, and as I 

 place Conrad's species, which is an entirely different thing, in the same genus, the 

 name mytilloides can not be used for it, and it must therefore take the next name 

 proposed, which is Conrad's cor. 



Dr. Lea admits Rafinesque's mytiUoides with doubt, and in his collection places 

 under that name specimens which I regard as a rather elongated Quadrula pyramidata. 

 Rafinesque's figure represents an elongated shell, almost absolutely straight on the 

 dorsal line, and with the beaks carried far in front of the rest of the shell. I have 

 never seen any thing which at all agrees with it. 



