206 



NORTH AMERICAN INDEX FOSSILS. 



55. R. grandis Vanuxem. (Fig. 239.) Devonic. 



Large, broadly elliptical. The direction of the foramen in the 

 pedicle valve is in the shorter diameter of the shell. 



Hamilton of New York, Ohio, Indiana, Kentucky. 



. - . • 



Fig. 

 Hall.) 



239. Roemerella grandis, a group of dorsal and ventral valves, X *• (Afte 



XXIII. Crania Retzius. 

 Nearly circular, inequivalved, with no pedicle opening but at- 

 tached by apex or by the entire surface of the pedicle (lower) valve 

 which is depressed, conforming to the surface to which it is attached. 

 Brachial (upper) valve conical with subcentral and posteriorly 

 directed beak. In each valve is a pair of widely separated muscle 



scars near the posterior mar- 



gin and a pair close together 

 near the center ; vascular sin- 

 uses digitate. Middle Cam- 

 bric-Carbonic. 



56. C. scabiosa Hall. (Fig. 

 240.) Ordovicic. 



Small, with irregular out- 

 line and thickened margins. 

 Brachial valve thin. Surface 

 of both valves usually marked 

 by strongly lamellose growth 

 lines. Found adhering to 

 brachiopods and sometimes unrecognizable because of their assum- 

 ing the surface features of the body to which they are attached. 

 Differs from C. modesta in that the average shell is larger and 

 more rugose. 



Fig. 240. Crania scabiosa, a number of 

 shells attached to a brachial valve of Rafin- 

 esquina alternata, the ornamentation of which 

 they adopt, X l - (After Hall and Clarke.) 



