PALEONTOLOGY OF NEW-YORK. 



Spirifer coiicinnus ( u. s.)- 



Plate XXV. Fia. 2 a- i; and Plate XXVIII. Fia. 7. 



Shell semicircular or semielliptical : extremities rounded or salient ; 

 valves almost equally convex. Ventral valve gibbous towards the beak : 

 beak more or less elevated above the hinge line, and abruptly incui'ved 

 at the apex : mesial sinus subangular, and produced into an angular 

 extension which is much elevated, and sometimes slightly incurved in 

 front. Dorsal valve very convex in the centre : beak scarcely incurved ; 

 mesial elevation obtusely and sometimes acutely angular. Hinge line 

 equal to or a little less than the width of the shell. Area of medium' 

 size, well defined, and extending to the extj^emities of the hinge line. 

 Surface marked by from twelve to fourteen rounded, little elevated, 

 simple costsD on each side of the mesial lobe and sinus ; concentrical- 

 ly marked by imbricating lamellae, which are striated upon their sur- 

 faces and granular on the edges. 



In many specimens there are faint iiidications of a fold on each side of the me- 

 sial sinus, and of several similar ones upon the corresponding mesial elevation : 

 this character, however, is not constant in the specimens examined. 



This species is subject to considerable variation in form, the length and breadth 

 being sometimes nearly equal, and the cardinal extremities rounded, while in other 

 specimens these are salient. I have seen two specimens only in the shaly limestone; 

 the ordinary position of this species being in the Upper Peutamerus limestone, as- 

 sociated with Pentamerus pseudogaleatus, etc. The finer surface markings do not dif- 

 fer very essentially from S. cyclopteriis, but the angular character of the sinus and 

 mesial fold with obscure plications, the much more elevated beak of the ventral 

 valve, and more numerous plications are distinguishing features. 



PLATE XXV. 

 Fig. 2 a - e. Views of a single large specimen from the shaly limestone. 

 Fig. 2 f. Enlargement of the surface. 



Fig. 2 g, h, i. Dorsal and front views of specimens from the Upper Pentamoras limestone. 



PLATE XXVIir. 



Pig. 7 a, h. Dorsal and ventral views of a larger specimen from the Upper Pentamerus 

 limestone. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 



group; Helderberg mountains and Hudson, rarely : Upper Pentamerus limestone; 



Schoharie and Helderberg mountains. 



