﻿4JS!S SYMl'llYNOTA 



and feeble; nacre l)Iuisli-\\liit(.', lurid in the cavities, with a dis- 

 tinct prismatic border. 



Length 65, height 40, diam. K) mm. /, ' 



Type locality, Eastern Tennessee. ri--(>^- 

 Mari:;aritana quadrata Li:a, IV. Ac. N. Sci. Phila., V, 1861, p. 



41 ; Jl. Ac. N. Sci. Thila.. 11, 1862, p. 210, pi. xxxii, fig. 279; 



Obs,, IX, 1863, p. 2,2, pi. xxxiF, fig. 279. 

 Mar gar on (Margaritana) quadrata LiiA. S\n., 1870, p. 68. 

 Margaritana (Alasmodonta } quadrata Cuessin, Conch. Cab. 



Ano., 1876, p. 2'/T,, pi. Lxxxiii, figs. 5. 6. 

 Symphynota quadrata Simpson, Syn., 1900, p. 664. 



This species approaches so nearly to Alasmidonta that it 

 might almost as well be placed in it as the present group, its 

 teeth are better developed than are those of any member of that 

 group, and the shell is more compressed. It approaches de- 

 corata, but the teeth are much less perfect. 



Subgenus Lasmigona Rafinesque, 1831. 



l.asiiiigona Rafinesque, Cont. Monog., 1831, p. 4. 



Shell subrhomboid. compressed, corrugated behind ; beaks 

 low, their sculpture consisting of several coarse ridges, which 

 generally fall into two slight loops, and often with radiating 

 ridges in front and behind ; epidermis shining ; laterals partly 

 developed, consisting of blurred ridges, which slope diagonally 

 downward and backward on the hinge plate ; cavities of the 

 beaks shallow ; dorsal scars faint, irregular. 



Animal with the marsupium occupying the whole of the out- 

 er gills, very thick, like that of Atiodonta : inner gills free all 

 or the greater part of their length from the abdominal sac ; 

 branchial opening papillose ; anal opening generally smooth 

 or only slightly crenulate. 



T}'pe, Alasuwdonta costata Rafinesque. 



vS\-MPiiYN()T.\ coS'i'A'i'A ( Rafines(|uc) . 



Shell long rhomboid, subcompressed, solid, ine(|uilateral. 

 with scarcely elevated, compressed beaks, their sculpture con- 

 sisting of a few strong, straight or slightly doublv-looped 



