240 Deifcn'j^fhns of Xtic SjH'cus of loi'sih. 



Stirptorhyiich us {Strophomemi) cloutjata — (J ARiKs) . 



Slu'll !?ubtripMi!il : rcsupiiiato, brondor tlisin Kitisr; ciinliiial Hikm^x- 

 toiulod boyoiul tlio width oi the shell tarthoi I'orwartl, dolKn'ti'd at the 

 anji'los ; sludl narriuving rapidly to tho iVont, giving it a triaugidav out- 

 lino. 



Ventral valvo concave ; hoak somewhat olovated and projecting, 

 minutely perforated; cardinal area rather wide, narrowing gently from the 

 beak to the extremities ; loramen triangular, closed. Interior showing 

 the hinge teeth prominent and sharp, subtrigoiial, roughly striated on 

 the cardinal line ; dental ridge extending forward, nearly inclosing an 

 (>val-shajied depression, divided by a slight mesial ridge ; cardinal mar- 

 gin linear anil iMominent ; outside of the oval-shaped depression, 

 towanl the free margins, in perfect specimens, the surface is coarsely 

 punctured, and the margins roughly thickened. 



Dorsal valve convex in the middle, sloping rapidly to the free mar- 

 gins ; depressed or nearly Hat on the umbone aiul at the beak ; a shal- 

 low mesial sinus, in some cases from the beak to the middle of the 

 shell; beak not projecting; cardinal line straight, linear. Interior 

 showing the cardinal process small, divided at the beak into two sharp 

 tooth-like parts, directed oblitpiely forward ; socket elevations promi- 

 nent, slightly obliiiue. Other interior features not observed. 



Both valves covered with fine radiating striiv of nearly uniform 

 size, increased by interstitial addition, and crossed by delicate concen- 

 tric lines. 



Breadrl\ of a large specimen, along the cardiunl line, isl^ inches ; 

 length, from beak to front, less than one inch. 



Position anil locality — upper part of the Cincinnati Group, in Ohio 

 anil Indiana. Collected by U. P. James. 



Strophomcim dceUvh — (James). 



This shell is remarkable for tlie manner in which it is arched or 

 bent i>ver. Cardinal line of the ventral valve straight ; area narrow ; 

 beak slightly projecting; cardinal line pointed at the extremities, ex- 

 tending, apparently, beyond the width of the shell below (owing to 

 the sudilen depression or curve of the lateral margins, directly forward 

 of the points of the cardinal line, it has this feature") ; lateral and front 

 margins bent over at nearly right angles with the plane of the exterior 

 of the valve. iShell slightly convex from the beak to the extremities 

 of the cardiiial line, and about two thirds of the distance from beak to 

 front, givintr to the umbonal convex surface a snbtriamridar form. 



