﻿I.AMPSILIS 



37 



with fine, doubly-looped beak sculpture: Carunculina is charac- 

 terized by small, dark shells with singly-looped beak sculpture, 

 and Proptera consists of generally large forms with a dorsal 

 wing and purple nacre. 



The shells of this genus are never arcuate, even in old age, 

 and never biangulate. The posterior ridge is often wanting, 

 and is seldom high or angulated. 



Key to groups of Lampsilis. 



Shell without a dorsal wing. 



Inflated, with coarse beak sculpture. 



Group of L. ventricosa. 

 Shell solid. 



Evenlv long elliptical, feebly dimorphic, rayed. 



Gr. of L. ligamentina. 

 Short elliptical, strongly dimorphic, smooth, feebly 

 rayed. Gr. of L. orbiculata. 



Male shell sinuate at post-base; female shell highest. 



Gr. of L. trabalis. 

 Small : beak sculpture singly looped. 



Gr. of Z,. texasensis. 

 Long elliptical, rayed. 



Thin, evenly rounded behind; female much swollen at 



post-base. Gr. of L. modioliformis. 



Rather solid, thinner behind, beak sculpture irregular. 



Gr. of L. iris. 

 Long or short elliptical, strongly dimorphic; female shell 



obliquely truncate behind. 

 Smooth, scarcely rayed. Gr. of L. anodontoides. 



Scarcely smooth. Gr. of L. subrostrata. 



Shell long, pointed behind. 



Very glossy, brightly rayed. Gr. of L. snban^jdata. 



Dull colored, feebly rayed. Gr. of L. cUipsiformis. 



Compressed, elongated, dull colored. Gr. of L. tiasuta. 



Shining, inflated, rayed, dimorp'hic ; pseudocardinals small. 



Gr. of L. hitcola. 



