﻿I.AMPSILIS 59 



Lampsilis biangularis (Lea). 



Shell elliptical, obovate or sttbrhomboid, generally inflated, 

 solid, with rather full but not high beaks, with a high, angled 

 posterior ridge and a lower one above it ending in a biangu- 

 lation at the posterior end a short distance above the base ; 

 epidermis smooth and shining in the younger shells, which are 

 greenish-yellow with faint broken dark rays ; in the old shells 

 it is dark, often blackish, and somewhat roughened ; ligament 

 large, feebly djeveloped in front of the beaks ; left valve with 

 two generally high and somewhat compressed, but sometimes 

 stumpy, pseudocardinals, the hinder under the beak, and two 

 rather distant laterals, the hinge line narrowed and rounded 

 in front of them ; right valve with one pseudocardinal with a 

 small one above it, and one high, truncate lateral ; beak cavities 

 rather deep and compressed ; muscle scars deep, smooth ; nacre 

 lurid, dull bluish, or purplish-white. The female shell has 

 only a slightly developed marsupial swelling. 



Length 95, height 62, diam. 35 mm. 



Length 90, height 50, diam t^J mm. 



Tennessee drainage. 



Type locality, Caney Fork River, Tennessee. 

 Unio biangularis Lea, Pr. Am. Phil. Soc, 1, 1840, p. 288. 

 Unio biangulatiis Lea, Tr. Am. Phil. Soc, VIH, 1843, P- ^97> 



pi. IX, fig. 8 ; Obs., in, 1842, p. 35, pi. IX, fig. 8. — Chenu, 



111. Conch., 1858, pi. XXX, figs. 7, ya, yb. — Kuster, Conch. 



Cab. Unio, 1861, p. 189, pi. i.x, fig. i ; pi. lxi, fig. i. — Sow- 



ERi'.Y, Conch. Icon., XVI, 1868, pi. i.xxx, fig. 421. 

 Margaron (Unio) bicmgulatus Lea, Syn., 1852, p. 38; 1870, 



p. 61. 

 Lampsilis biangulatiis Simpson, Syn., 1900, p. 533. 



A very variable species in form, epidermis and solidity. It 

 probably groups here, though its relations are not very close 

 to any other members of this assemblage. It is sometimes 

 difficult to separate specimens of this species from L. perdix, 

 which I have placed in the ligamentina group. 



