706 PBOCEEDINGS OF THE NATIONAL MUSEUM. yol.xxii. 



slope radially plicate ; epidermis dark; pseudocardinals stum i)y, radial, 

 graimlarly striate; laterals double iu the left valve, single in the right, 

 with a faint, secondary ridge below; anterior muscle scars deep, nearly 

 smooth ; cavity of the beaks moderate, slightly compressed. 

 Animal unknown. 



tUNIO SLOATIANUS Lea. 



*Unio sloatianus Lea, Pr. Am. PhiL Soc, I, 1840, p. 287; Tr. Am. Phil. Soc, 

 VIII, 1842, p. 217, pi. XVI, fig. 33; Ob8.,III, 1842, p. 55, pi. xvi, fig. 33.— 



* H. and A. Adams, Gen. Rec. Moll., II, 1857, p. 497. -* Chenu, 111. Conch. 1858, 

 pi. xxxii, figs. 7, 7a, 76.—* Kuster, Conch. Cab., 1862, p. 286, pi. xcvi, fig. 3. — 

 ^B. H. Wkight, Check List, 1888.— *P^tel, Conch. Sam., Ill, 1890, p. 167. 



* Margaron ( Unio) sloatianus Lea, Syu., 1852, p. 21 ; 1870, p. 31. 



* Pleciomeriis sloatianus Conrad, Pr. Ac. N. Sci. Phila., VI, 1853, p. 261. 



* Unio atromarginatus Lea,' Pr. Am. Phil. Soc, I, 1840, p. 288; Tr. Am. Phil. Soc, 



VIII, 1842, p. 207, pi. XIII, fig. 21; Obs., Ill, 1842, p. 45, pi. xiii, fig. 21.— 



* H. and A. Adams, Gen. Rec Moll., II, 1857, p. 488.—* Chenu, 111. Conch., 1858, 

 pi. xxviii, figs. 6, 6a, 66. — * Kuster, Couch. Cab. Unio, 1861, p. 250, pi. 

 Lxxxiv, fig. 2.— *B. H. Wright, Check List, 1888. — *P^tel, Conch. Sam., 

 Ill, 1890, p. 145. 



* Margaron ( Unio) atromarginatus Lea, Syn., 1852, p. 19; 1870, p. 29. 



* Pleciomerus atromarginatus Conrad, Pr. Ac N. Sci. Phila., VI, 1853, p. 260. 



* Unio aratus Conrad, Ann. and Mag., IV, 1849, p. 302; *Pr. Ac. N. Sci. Phila. IV, 



1849, p. 154. 



* Unio plectophorus-CoNRAV), ,J1. Ac. N. Sci. Phila., 1, 1850, p. 277, pi. xxxviii, fig. 7. 



* Plectomerus plectophorus Conrad, Pr. Ac N. Sci. Phila., VI, 1853, p. 2. 



Chattahoochee and Flint rivers, Georgia. 



(Group of Unio crassidens.) 



Shell generally solid, rather inflated, rhomboid oval, with a sharp, 

 well-developed posterior ridge; beaks prominent, the sculpture consist- 

 ing of a few coarse ridges running nearly parallel with the growth 

 lines and swollen at the posterior ridge; surface of the valves nearly 

 smooth or only marked by growth lines; posterior slope beariDg 

 wrinkled, corrugate, radiate ridges; epidermis often faintly rayed. 



Animal having the branchiie very large, rounded below, inner the 

 larger, free nearly or quite their entire length from the abdominal sac; 

 branchial and anal openings large, with many small papillae ; marsupium 

 occupying the entire outer gills. 



fUNIO CRASSIDENS Lamarck. 



*Unio crassidens Lamarck, An. sans Vert., VI, 1819, p. 71. — * Lea, Obs., I, 1834, 

 p. 199.— *Deshayes, An. sans Vert., 2d ed., VI, 1835, p. 532; 3d ed., II, 1839, 

 p. 667.— *Hanley, Test. Moll., 1842, p. 184 ; ' Biv. Shells, 1843, p. 184, pi. xx, 

 fig. 46. — * Catlow and Reeve, Conch. Nom., 1845, p. 58. — *H. and A. Adams, 



^ 1 Lea's type of sloatianus is an old, arcuate shell, while the type of atromarginatus 

 is young and quite different looking. But the young plicate atromarginatus gradually 

 changes into the smoother sloatianus as it grows older, nnd specimens of both show 

 the dark bordered nacre, though it is mure prououuced in the young shells. 



I 



