SHUMARD AND SWALLOW—NEW FOSSILS. 213 
Myartmva Kansasensis, Shumard. 
Shell sub-rhomboidal, sub-inequivalve, inequilateral, gibbous, 
the left valve Agee gibbous than the right; height about dude 
the len sn eb ung specimens the greatest len: ‘ont is at the 
cardina border, tint in the adult towards the p: argin ; 
cardinal margin oblique, slightly arched, and Reanieg with the 
posterior atid ge angle of about 120°; posterior margin 
rather strong] ite in adult specimens, and very gently 
rounded in t ol cd ; palleal margin rounded ; buccal ‘livia 
= gig Sean 3 prominent anteriorly, and dec 
margin; anterior 
very abrupt; sks terminal, attenuated, directed obliquely 
forward, incurved; surface with sttong, imbricating, sub- 
equidistant, concentric elle, whose free edges are often 
e car 
imber with the age of the ey beneath these is a 
rather broad, smooth space, which i is continuous with a similar 
ape extending from as Gatien! region. ‘Each valve exhibits a 
single muscular im; impression, which is large, ovate, and situated 
towards the Lage margin. 
Height, 2 iachons ‘ ene 17.3. anihane, 
