﻿LAMPSTLIS 129 



This species sometimes exceeds the above dimensions and 

 is occasionally one of the most ponderous of North American 

 Uiiiones. Other specimens, in unfavorable conditions, no doubt, 

 do not exceed a length of 35 to 40 millimeters and are rather 

 thin. 



LampsiIvIS pi.easii (Marsh). 



Shell small, long elliptical, suboompressed, scarcely subsolid, 

 with low beaks, their sculpture not seen ; growth lines irregu- 

 lar ; surface dirty tawny with numerous close, narrow, wavy 

 rays, the whole dull co'lored and somewhat cloth-like ; posterior 

 ridge low, rounded; left valve with two irregular, somewhat 

 compressed pseudocardinals and two rather feeble, short lat- 

 erals ; right valve with one pseudocardinal, a faint one above it, 

 and one lateral ; beak cavities shallow, with a few deep pits ; 

 anterior scars separate ; nacre lurid greenish, bluish or brown- 

 ish, slightly thickened in front. The shells of this species are 

 somewhat drawn out behind and bluntly pointed about midway 

 up from the base. The base line is rounded and a little full 

 just behind the center; that of the female differs but little from 

 the male, it being sHghtly more produced in the region of the 

 marsupium. 



Length 40, height 2^, diam. 13 mm. 



Type locality. Little Red River, Arkansas. Also, Morrisville. 

 Polk County, Missouri. 

 Unio pleasii Marsh, the Observer (a newspaper), H, May, 



1891 ; Nautilus V, 189 1, p. 2. 

 Lampsilis pleasii Simpson, Syn., 1900, p. 557. 



All the specimens I have seen of this little species are in rath- 

 er bad condition, being greatly eroded. I cannot be certain 

 as to what the alliances are, but presume that it is related to L. 

 eHipsiformis. It is smaller, more delicate and thin than that 

 species, and the nacre is quite different. 



Lampsilis ARKANSASENSis (Lea). 



Shell ovate, subsolid, subinflated with a low, almost double 

 posterior ridge, which ends in a slight biangulation behind 

 about midway up from the base ; above this posterior pomt 



