DvM'Tiptioii* of K'^w Sp^xMi» of FomlU. 241 



y{(.Tc. -tl -ir. I.', If -tlu. Mit-i of tb« i^bell if bent suddeiily ovfer. Burfkc*- 

 c>. ling ptria;, a oesutral and FtroDg OBe mor^ 



jMiOHiiiieiit tban tbe others ; abotit everj fourth or fifth striae larger 

 than the ones between ; crossed hy fi^ne con centric liEes. Btria; iii- 

 creased hj interstitial addition. Dorsal valve not observed. 



Width, measuring aiong the cardinal jixie, seven eigbtlis of an inch : 

 length about the «ame. , 



Fo.-itioTi an<3 loeality — Cincinnati G-rouj), near Boyd's station, on th- 

 K<-ijtucky Central Kailroad, about 30 miles south of CincinnatL 



Co]] '-'-ted by U. P. James. 



Slr^'torh^ncJius ( Strop homcwi) oatusta — (J AMES J. 



Shell subquaidrate, or semi-oval, resupinate, cardinal line varyinir 

 from a -kittle less to a little more tlian the width (if the shell farthej- 

 forward, deflected at the extremities- Ventral valve broadl}^ concave : 

 beak, in old specimens, promraent and projecting, perforated ; cardinal 

 area broad in the middle, narrowing to tbe extremities ; foramen tri- 

 angular, closed ; from six to sixteen strong plications at right angles, 

 or sloping inwardly along the cardinal line. Interior — Cardinal edgt- 

 prominent ; hinge teeth sharp, oblique ; dental ridge encirclrDg a sau- 

 cer-shaped cavity, open in front, with rather an obscure mesial ridg<- 

 and coarse oblique striae. The whole interior outside of the cavity 

 sh^we a rough or coarsely punctured surface. 



Dorsal valve slightly convex on the disk, sloping to the free mar- 

 gins, and curving upward at the extremities of the cardiual line ; flat 

 or depressed near the beak ; cardinal line nearly striught, area lineaj- : 

 plications as on the other valve. Interior — Cardinal process bifid, 

 prominent; sockets trigonal, rather deep, oblique ; socket ridges prom- 

 inent ; four or five longitudinal ridges commencing just below the caj- 

 <linal process, extending about two thirds of the distance to the front : 

 other parts of the surfac.e, to near the free margins, roughly granu- 

 lated ; striated along the lateral and front margius. 



Surface of both valves fexterior) covered with rounded radiating 

 striae, increased Ij}^ implaiitation, of nearly uniform size in some cases, iii 

 others alternating, or every third or fourth one stronger than the one> 

 between, crossed by fine concentric striae, which, in some nf thf oldf-t- 

 specimens, is rather obscure. 



Breadth of a large specimen, on the cardinal line, 1^ inche'S ; length . 

 1^ inches. There is, however, some variation in these proportions, 

 and some r»f the young shells are not much over half an inch each 

 wav. 



