64 [ Senate 



CyRTIA DALjNLVNI. 



Pal. N.Y. Vol. iii, pi. 24, f. 2. 



Shell trigonal ; valves extremely unequal : ventral valve tri- 

 angularly pyramidal : dorsal Vcilve semicircular; mesial lobe 

 flat, or with a slightly depressed line; beak scarcely defined, 

 or rising above the hinge-line ; hinge-line straight ; area tri- 

 angular, Hat or slightly arcuate ; foramen narrow, linear, usually 

 closed in the lower part, with a semitubular opening above ; 

 concentric lamellse strong, and often very conspicuous near the 

 margin. Surface granulose-punctate. 



This species differs from the Cyrtia {Spirifer) pyramidalis of the Nia- 

 gara group ; having the dorsal valve more uniformly convex, the mesial 

 fold broader and more prominent ; while the depressions are not so deep, 

 the mesial sinus is broader, the plications bounding it are less conspicuous, 

 and the concentric imbricating lamellae are stronger in the species under 

 consideration than in the Niagara species. 



I have heretofore referred this species, with doubt, to the C. heteroclitus 

 of Europe; for among the variety of forms referred to this species, it is 

 difficult to know the typical one. It differs, however, from the Eifel species 

 of that name. 



Geological position and locality. Limestones of the Lower Helderberg 

 group, Albany and Schoharie counties. 



Cyrtia rostrata ( n. s.). 



Pal. N.Y. Vol. iii, pi. 100, f. 5. 



Shell semicircular or triangular : ventral valve much elevated 

 at the beak, a distinct sinus extending from beak to front ; beak 

 simple, angular, not incurved : dorsal valve depressed-convex, 

 semicircular ; mesial fold moderately elevated, slightly flattened 

 and marked with a faint longitudinal depressed line ; beak 

 scarcely elevated above the cardinal margin ; hinge-line straight, 

 equalling the greatest width of the shell ; area broad triangular, 

 plane, or rarely subarcuate ; foramen narrow, extending to the 

 apex of the beak of the ventral valve, partly closed above by a 

 central plate. Surface marked by nine to eleven elevated an- 

 gular costa3 on each side of the middle, crossed by strong im- 

 bricatinG; concentric lamellse. 



