36 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



ORTHIS LIVIA. 



Orthis livia : Billings, Canadian Journal, No. xxvii, p. 266. 



Two individuals, apparently of this species, have been found in Western 

 New- York. It has a larger area and much coarser striaa than the O. vanu' 

 zemi and some others of similar character. 



GENUS STEOPHODONTA ( Hall). 



The Schoharie grit has afforded characteristic examples of se- 

 veral species of this genus which are known in the higher rocks, 

 or as ranging through the Upper Helderberg limestones and the 

 Hamilton group. Among these are Stropliodonta demissa, S. inequi- 

 striata, and S. crenistria = S. fragilis. There are, besides these 

 and some other known species, several very distinct forms which 

 are known only in the. condition of casts, 



STEOPHODONTA ALVEATA ( n. s.). 



Casts of the ventral valve nearly flat, and varying to slightly 

 concave or convex ; semielliptical in form, the hinge-line equal- 

 ling or sometimes a little less than the greatest width of the 

 shell, crenulated. Muscular impression strongly marked ; the 

 sides very straight and limited by a deep groove, divided along 

 the middle, and each side bilobed at the lower margin. Near 

 the exterior margin of the valve there is a depression reaching 

 from the hinge-line entirely around the front of the shell, in- 

 dicating a thickening upon the interior of the valve, which is 

 marked by the striae, and by vascular impressions in well- 

 preserved specimens. . 



The cast of a dorsal valve (found with the ventral valves) of the 

 same form, shows the submarginal callosity, a crenulated hinge 

 line and double cardinal process, with a muscular impression 

 similar to that of the dorsal valve of S, rugosa. Length from 

 one-half to three-fourths of an inch, with a greater breadth. 



Geological formation and locality. In the Schoharie grit : at Clarksville 

 and Knox, Albany county. 



STEOPHODONTA CALLOSA ( n. s.). 



Casts of the ventral valve semielliptical, longer than wide, or 

 sometimes with length and breadth nearly equal, very convex 



'* or gibbous ; width across the middle of the valve, greater than 

 at the hinge-line and a little below ; area wide j hinge-line 



