202 



NORTH AMERICAN INDEX FOSSILS. 



42. T. ottawaensis Billings. (Fig. 235, c.) Ordovicic 



About one inch in diameter. Surface covered with fine radiat- 

 ing striae and crossed concentrically by fine discontinuous ridges. 



Trenton and Lorraine of New 

 York, Kentucky, Minnesota, On- 

 tario, Anticosti. 



43. T. terminalis Emmons. 



Ordovicic. 



About half as large as the preced- 

 ing or smaller ; foraminal slit flanked 

 by broad depression. Apex of bra- 

 chial valve marginal, not projecting. 



Trenton of New York and Canada. 





Fig. 235. a, b and d, Trematis 

 millipunctata, profile and ventral view, 

 X f an d enlargement of surface, X 

 16; c, Trematis ottawaensis, brachial 

 valve, X %• (After Hall and Clarke. ) 



44. T. millepunctata Hall. (Fig. 

 235, a-b, d.) Ordovicic. 



Intermediate in size between th< 

 two preceding ; foraminal slit deep, 

 beak of brachial valve projecting. Surface punctate. 



From the Utica and Lorraine of Cincinnati, O., and Coving- 

 ton, Ky. 



XVI. Schizocrania Hall and Whitfield. 



Subcircular, strongly inequivalve. Pedicle or lower valve flat 

 or concave ; a deep, broad triangular notch extends from near the 

 subcentral beak to the margin where it constitutes about one sixth 

 of the periphery. In the apex of this notch is a triangular trans- 

 verse plate extending about one third the distance to the margin. 

 Surface covered with concentric lines. Brachial valve convex; 

 larger than the pedicle valve and extending beyond it on all sides. 

 Beak marginal or submarginal. Surface with radiating striae. 

 Ordovicic and Devonic. 

 45. S. filosa Hall. (Fig. 236, a.) Ordovicic. 



Slightly ovate. Surface of brachial or upper valve covered with 

 fine, even, radiating striae. Pedicle valve strongly marked by irreg- 

 ular concentric undulations. This species is usually found attached 

 to brachiopods, particularly to Rafinesquina alternata. 



Trenton-Lorraine of New York, Ohio, Minnesota, Ontario. 



XVII. Lingulodiscina Whitfield. 

 Upper (brachial) valve linguloid with nearly terminal beak in 

 typical species ; lower (pedicle) valve discinoid with centrally placed 



