672 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



Tennessee and Cumberland river systems. 

 Untigared species. 



Margaritana etoivaJiensis Conrad, Pr. Ac. Nat, Sci. Pliila., IV, 1849, p. 154. ^ 

 Etowah Kiver, Georgia. 



Subgenus BULLELLA Simpson, 1900. 

 (Type, Margaritana arcula Lea.) 



Shell thin, greatly inflated, somewhat triangular, with a high, sharp 

 posterior ridge; beaks very full, having exceedingly strong, concen- 

 tric sculpture, extending well on to the disk; ]3seudocardinals reflexed, 

 compressed. 



Animal with the gills large, nearly semicircular below, inner the 

 larger, united the whole length to the abdominal sac; mantle border 

 with square spots.^ 



tALASMIDONTA ARCULA Lea. 



"^ Margarita {Margaritana) arcula Lea, Syu., 1836, p. 43; 1838, p. 27. 



* Margaritana arcula Lea, Tr. Am. Phil. Soc.,VI, 1838, p. 71 , pi. xxii, fig. 69 ; * 01)s., 



II, 1838, p. 71, pi. XXII, fig. 69.—* Troschel, Arch. fiir. Nat., V, 1893, Pt. 2, p. 

 238.—* Chenu, Mau., 1859, II, p. 144, fig. 712.—* B. H. Wright, Check List, 

 1888.— * P^TEL, Conch. Sam., Ill, 1890, p. 172 



* Unio arcula Hanley, Test. Moll., 1842, p. 210; Biv. Shells, 1843, p. 210, pi. xxii, 



fig. 49. — * Catlow aud Reeve, Couch. Nom., 1845, p. 56. — * Sowerby, Conch. 

 Icon., XVI, 1866, pi. xlviii, fig. 259. 



* Margaron (Margaritana) arcula Lea, Syn., 1852, p. 42; 1870, p. 67. 



* Alasmodonta arcula Conrad, Pr. Ac. N. Sci. Phila., VI, 1853, p. 262. 

 " Bap Ilia arcula H. and A. Adams, Gen. Rec. Moll , II, 1857, p. 500. 



* Margaritana (Alasmodonta) arcula Clessin, Conch. Cab. Auo., 1876, p. 272, pi. 



Lxxxiii, figs. 7,8. 

 Altamaha River, Georgia. 



tALASMIDONTA TRIANGULATA Lea. 



"" Margaritana iriangulata Lea, Pr. Ac. N. Sci. Phila., II, 1858, p. 138; * Jl. Ac. N. 



Sci. Phila., IV, 18.59, p. 228, pi. xxxii, fig. Ill; *Obs., VII, 1859, p. 46, pi. 



xxxii, fig. 111. — * Kuster, Conch. Cab. Unio, 1862, p. 303, pi. c, fig. 6.—* B. H. 



Wright, Check List, 1888. 

 *Unio triangulata Sowerby, Conch. Icon., XVI, 1868, pi. lxxx, tig. 414. 

 ^Margaron, (Margaritana) triangulata Lea, Syn., 1870, p. 68. 

 ^Margaritana triangxilatus P^etel, Conch., Sam., Ill, 1890, p. 174. 



South Carolina and Georgia. 



The following species are unknown to me: 



* Alasmodon (Decnramhis) atropurpureum Rafinesque, Cont. Monog., 1831, p. 5. 

 *Alasmodon. (Becurambis) scriptum Rafinesque, Cont. Monog., 1831, p. 5. 



1 Allied to ravenelianus Lea, according to Conrad. 



-In the only gravid specimen seen the outer gills were curiously wrinkled and 

 folded longitudinally, though the inner gills were plain. If this were a normal 

 character it would entitle the species to generic rank, but I can not feel certain that 

 it is. A. triangulata seems to stand between this and the ordinary Alasmidontas. 



