﻿LAMPSILIS 193 



Lampsii.is pi.anivalvis (Morelet). 



Shell eomewhat elongated, rhomboid, greatly compressed, 

 with a slight wing in front and a moderately developed one be- 

 hind, with a low, but distinct, angular posterior ridge; beaks 

 low, not inflated, but sharply pointed ; surface with fine growth 

 lines and slightly radially ridged in the umboual region ; epi- 

 dermis brown-olive ; left valve with a thick anterior pseudocar- 

 dinal, and an almost obsolete posterior one. with two lamellar 

 laterals ; right valve with two short pseudocardinals, the upper 

 smaller, and a long, curved lateral ; muscle scars shallow ; beak 

 cavities not deep ; nacre white. 



Length 66, height 35, diam. 14 mm. 



Usumacinta River, Guatemala. 

 Unio planivahis Morelet, Test. Noviss., II, 185 1, p. 24. — 



Fischer and Crosse, Miss. Sci., II, 1894, p. 560, pi. lix, 



fig. 2. 

 LMmpsilis planivah'is Simpson, Syn., 1900, p. 576. 



This species is greatly compressed, and has a decided wing 

 in front and behind on the dorsal portion. Like all the other 

 species of the group the general surface of the umbonal region 

 is compressed, but the beaks themselves are elevated into a 

 fine point. 



The shell figured by Fischer and Crosse is probably that of a 

 male. 



Lampsilis delphinulus (Morelet). 



Shell with a somewhat triangular outline, thin and much 

 compressed, the body of it elongated subrhomboid, with a near- 

 ly parallel dorsal and ventral lines when freed from the wing, 

 bearing a greatly elevated, somewhat triangular posterior dor- 

 sal wing and a small anterior one, whose dorsal line is parallel 

 with that of the base ; beaks low and compressed, with scarcely 

 any sculpture ; posterior ridge low, double or treble, ending be- 

 hind in a blunt, somewhat rounded point about at the median 

 line ; surface dull, greenish-yellow or brown, with faint rays. 



