﻿130 I,^^IPSIIJS 



there is a slight oblique truncation and at tlie posterior end of 

 the ligament there is an anti^le ; the central base is full and from 

 this point to the posterior end the outline is a little incurved : 

 beaks probably only moderately full, in the only specimen seen 

 much eroded : surface irregularly concentrically striate, green- 

 ish-tawny with very faint wavy rays behind ; left valve with 

 two nearly equal, small, biangular pseudocardinals and two 

 short, club-shaped laterals; right valve with two pseudocardi- 

 nals, the upper small and compressed, with one lateral and a 

 vestige of another below it ; beak cavities not deep, compress- 

 ed, with several small scars ; muscle scars well impressed ; 

 nacre silvery with a faint reddish or brownish tint, iridescent 

 behind, slightly thicker in front ; pallial line well marked, cre- 

 nate. 



Length 40, height 28, diam. 18 mm. 



Type locality. Hot Springs, Arkansas. Also, Saline River, 

 near Benton. Arkansas. (Call.) 



Unio arkansascnsis Lea, Pr. Ac. N. Sci. Phila.. \ I, 1862, p. 

 169; Jl. Ac. N. Sci. Phila., V, 1862, p. 206, pi. xxx. fig. 275; 

 Obs., IX, 1863, p. 28, pi. xxx, fig. 275. 

 Lampsilis a rkansos crisis Simpson. Syn., 1900, p. 557. 



I have seen only one specimen that I feel sure is this shell. 

 the type, and tliis is apparently a male shell. The whole um- 

 bonal region is badly eroded, and it is not in the best condition 

 generally, yet I know of nothing it can be referred to. It seems 

 to be a member of the ellipsiformis group. 



Grou]) of Lampsilis ocarkcusis. 



Shell elliptical, rather solid, subcompressed, with low beaks 

 slightly biangulate behind and showiing the rest periods quite 

 plainly. Pseudocardinals subcompressed ; laterals rather long, 

 extended forward to near the pseudocardinals, the groove be- 

 tween the two in the left valve extending forward behind the 

 pseudocardinals and filled with epidermal matter ; nacre wliit- 

 ish-silven- : male and female shells but slightly different. 



