CONTRIBUTIONS TO PALAEONTOLOGY. • 31 



rounded, the posterior one least curved : margins thickened. 

 The impressions of the anterior muscles are nearly united in a 

 transversely subelliptical scar : posterior adductor scars dis- 

 tant, not well defined in the specimens. 

 No other species of this or any other species of the genus are known to 



me at this time, from the Upper Helderberg group. 



Geological formation and locality. In the Schoharie grit, in the town of 



Knox, Albany county. 



" CRANIA GREGARIA ( n. s.)." 

 Shell small, obliquely very depressed-conical, subcircular or ob- 

 late, narrower at the posterior end ; apex at the posterior third 

 of the shell. 

 Surface apparently smooth. 



This small species occurs from the size of a pin's head, to those having 

 a transverse diameter of a little more than a tenth of an inch, with a lon- 

 gitudinal diameter a little less than one-tenth of an inch. On a single valve 

 of a large bivalve shell, nearly forty individuals of this species can be seen^ 

 together with the remains of several ventral valves of one of the larger 

 species. 



It may be possible that these small fossils are the young of C. hamiltonice, 

 which have commenced their existence upon the same body which sustained 

 the parent shells. 



Geological formation and locality. In the shales of the Hamilton group, 

 in Bristol, Ontario county. 



GENUS PHOLIDOPS (H/^ll). 

 " PHOLIDOPS AREOLATA ( n. s.)." 

 Shell broadly subovate or scarcely circular, wilder on the poste- 

 rior third, broadly rounded behind and more narrowly rounded 

 in front. 



The cast of one valve ( the dorsal valve? ) shows a deep ovate 

 or subcordiform muscular scar, which is nearly surrounded by an 

 elevated areola, and partially divided by a median ridge from 

 above. The opposite ( ventral? ) valve has a larger muscular scar, 

 which is auriculate above, with the surrounding areola divided 

 at the lower or anterior margin. Surface somewhat abruptly flat- 

 tened on the posterior side, and more gently sloping on the front 

 of the valve. 



One specimen has a length a little less than one-fourth of an 

 inch, with a width across the middle nearly the same. The only 

 specimens known in the Schoharie grit are casts, and we have 

 not therefore seen the exterior of the shell. In casts of two in- 



