208 NORTH AMERICAN INDEX FOSSILS. 



61. C. modesta White and St. John. (Fig. 466, d.) 



Upper Carbonic. 



Average diameter y 2 inch. Brachial valve moderately convex. 

 Surface concentrically striated. 



Ohio, Indiana, Iowa, Kansas. 



XXIV. Craniella CEhlert. 



Large, subcircular or subquadrangular. Pedicle (lower) valve 

 thin, adhering by its entire surface. Brachial (upper) valve con- 

 ical with subcentral and posteriorly directed apex. Muscle scars 

 similar to Crania. Differs from Crania in the vascular sinuses of 



FlG. 244. /, 2, Craniella hanriltonice, top and lateral view of dorsal valve ; j>, a group 

 of ventral valves attached to shell of Cypricardella bellistriata, X *• (After Hall.) 



the brachial valve being S-shaped ; they start from near the pos- 

 terior muscle scars and extend to the anterior portion of the valve, 

 sending to the sides of the valve dichotomizing secondary branches. 

 Ordovicic-Devonic. 



62. C. hamiltoniae Hall. (Fig. 244.) Devonic. 



Subcircular. Brachial valve nearly conical with subcentral 

 apex, pointed in well preserved specimens. Exterior marked by 

 concentric lamellose striae. Pedicle valve marked by four strong 

 adductor muscle impressions and by digitate vascular impressions. 



Hamilton of New York ; Hay and Athabasca rivers, Canada. 



XXV. Pholidops Hall. 



Small, ovate, unattached, equivalved and equiconvex; without 

 pedicle opening. The edges of the valves are flattened where they 

 join. The interior of each valve is marked by an elevated and 

 sharply defined muscular impression which is subtriangular with 

 the apex of the triangle pointing anteriorly. Ordovicic-Devonic. 



