386 NORTH AMERICAN INDEX FOSSILS. 



34. T. subemarginata (Conrad). (Fig. 488, d.) Devonic. 



From the beak a flattening or depression extends to both the 

 anterior and the posterior margin. Type of genus. 



Hamilton : New York, Pennsylvania. 



XV. Cardiomorpha de Koninck. 

 Equivalve, inequilateral, oval, gibbous. Beaks almost at the 

 anterior extremity, prominent, spirally enrolled toward the front. 

 Hinge line thin, arched. Hinge margin in- 

 flected nearly at right angles to form a hollow 

 lunette extending from the beak nearly to the 

 cardinal angle. Hinge teeth absent. Pallial 

 Fig. 490. Cardio- Hne simple Ordovicic to Carbonic. 



morpha missourien- 



sis. (Kan. Pal., 35. C. missouriensis Shumard. (Fig. 490.) 

 VI /"0 Carbonic. 



Surface marked with fine and crowded concentric striae. 



Coal measures of Illinois, Kansas, Missouri, Nevada. 



XVI. Cardiopsis Meek and Worthen. 



Valves gibbous, inequilateral, subcircular, with short hinge line 

 and prominent and incurved beak. Surface marked with radiating 

 striae or costae and with concentric growth lines. Hinge with one 

 or two cardinal teeth. 



Differs from Cardiomorpha in the presence of cardinal teeth and 

 radial sculpture. Miss. -Carbonic. 



36. C. radiata Meek and Worthen. (Fig. 488, e.) Mississippic. 

 Costae sharp, alternating in part. Type of the genus. 

 Kinderhook : Indiana, Illinois. 



XVII. Psiloconcha Ulrich. 

 Shell very thin, elongate, inequilateral, gaping slightly at both 

 ends. Hinge plate very narrow, without 

 teeth. Ligament internal, linear. Mus- 

 cular impressions very shallow, the poste- 

 rior three times the length of the anterior. 

 Pallial line simple. Ordovicic. Fig. 491- Psiloconcha inor- 



nata. (After Ulrich, Pal. 



37. P. grandis Ulrich. (Fig. 489, d-e.) ., vn.) 



Ordovicic. 

 Posterior margin regularly rounded ; anterior angular. 

 Upper beds of Cincinnati Group of Ohio. 



