﻿AT.ASMIDONTA 495 



Mar gar on (Margaritana) undiilata LiiA, Syn., 1852, p. 42 ; 



1870, p. 68. 

 Mya undulata Wood, Ind. Test. Rev., 1856, p. 199, pi. i, supp,, 



fig- 5- 

 Baphia undulata H. and A. Adams, Gen. Rec. Moll., 11, 1857, 



p. 499. 



Unio undulatus Cati^ow and Reeve, Conch. Nom., 1845, P- ^5- 



Strophitus undulatus Stimpson, Shells of New Eng., 1851, p. 



15- 

 f Unio glabratiis Sowerbv, Rec. and P'oss. Shells, XVI, 1823, 



Alasmodonto sculptilis Say. N. Harmony Diss., II, 1829, p. 



339 

 Strophitus sculptilis Stimpson, Shells of New Eng., 185 1, p. 



15- 

 Unio hians Valenciennes, Rec. Obs. Zool., 11, 1833, p. 235, 



pi. liv, figs. 2a, 2b. 

 Uniopsis radiata Swainson, Tr. on Mai., 1840, p. 289, fig. 62, 

 Uniopsis niytiloidcs Swainson, Tr. on Mai., 1840, p. -i^d^i, fig. 



62. ' . ^ ^ 



? Unio szi'ainsoni Sowerby. Conch. Icon., XVI, 1868, pi. lxxvi,. 



fig. 396. 

 Margaron (Margaritana) szvainsoni I^ea, Syn., 1870, p. 30. 



A characteristic species of the Atlantic drainage. Usually 

 the shell is solid and shining, brightly rayed when young but 

 becoming apparently a uniform brown or blackish when old. 

 but showing rays when held up to the light. The beak sculp- 

 ture is very coarse and there are sometimes radial wrinkles 

 running across it. The teeth are stronger than in any other 

 species, which 1 place in Alasmidonta. The nacre varies much 

 in color and is decidedly thickened in front. 



Subgenus Pressodonta Simpson. 1900. 



Pressodonta Simpson, Syn.. 1900, p. 667. 



Shell decidedly rhomboid, surface generally painted with 

 unbroken rays ; beak sculpture slightly corrugated ; teeth com- 

 pressed. 



Marsupium thick, smooth, pad-like. 



Type, Unio calccohis Lea. 



