﻿250 MlvUIONIDUS 



Cardinal teeth qreiutlate, erect, rather compressed, those in the 

 left valve nearly on the same line; lateral teeth slender, straight 

 and nearly smooth. Anterior cicatrices well impressed, pos- 

 terior cicatrices diistinct, dofsal cicatrices un)der the plate 

 behind the cardinal teeth. Beak cavity rather shallow, cavity 

 of the shell deep and uniform. Nacre bluish-white, rather 

 thicker anteriorly. 



Length 36, height 19, diam. 13 mm." (Walker). 



Type locality, Calvary, Georgia. 

 Medionidus simpsonianiis VVai.kkk, Naut., 1905, XVIII, p. 



136, pi. IX, figs. 4-5. 



"This species belongs to the conradicus group of Medionidu>s 

 as defined by Simpson, and is most nearly related to M. pen- 

 icillatus. I'ut it differs decidedly from all the described spe- 

 cies in the compression of the anterior end, the elevation of 

 the superior-anterior margin and the regularly rounded pos- 

 terior margin, which is equally curved above and below, the 

 tip being on the median line and not depressed towards the 

 basal margin as in all the allied species. The ridges on the 

 posterior slope are quite strong, but not so numerous as in 

 M. kingi." 



Mkdionidus kingi (B. H. Wright). 



Shell small, elongate, solid and somewhat inflated, with a 

 well-developed posterior ridge, which is bluntly angled or 

 rounded, with rather full, high beaks, whose sculpture con- 

 sists apparently of slightly tloul>ly-looped ridges ; posterior 

 slope having strong, curved, radial ribs ; there are sometimes 

 a few slight corrugations on the body of the shell ; surface 

 hardly shining, tawny, with feeble, broken, dark rays, which 

 are often split up into wavy, irregular hair lines ; pseudocardi- 

 nals small, solid, triangular, two in the left valve and one in 

 the right ; there are two slender laterals in the left valve and 

 one in the right ; anterior scars well marked ; posterior scars 

 shallow : nacre lurid purple, iridescent behind. The male 

 shell is somewhat arcuate, its rounded posterior point being 



