BRACHIOPODA—ATREMATA. 195 



C. Wedge-shaped, with very acute beaks III. 



III. Valves convex 3. 



3. Large 25. L. cuneata. 



3. Minute 28. Z. spatulata. 



III. Valves depressed 19. L. trentonensis. 



D. With converging but straight sides IV. 



IV. Beak obtuse, large 21. L. eva. 



17. L. cobourgensis Billings (Fig. 228, a-b.) Ordovicic. 



Large, oval. Both valves moderately convex. Length about one 



fourth greater than width. Concentric growth lines fine, becoming 



FlG. 228. a-b, Ling ula cobourgensis; c, L. rectilateralis. All natural size. (After 



Billings Can. Geol. ) 



sharp. Elevated and closely crowded striae on the lateral slopes. 

 Trenton of Minnesota, southeastern Canada. 



18. L. curta Conrad. Ordovicic. 

 Small, obtusely ovate, depressed convex. Length and breadth 



nearly equal. Beaks scarcely projecting beyond the margin of 

 the shell. Front broadly rounded. Surface covered by elevated 

 concentric lines. 



Trenton-Utica of New York, Pennsylvania, Quebec, Frobischer 

 Bay. 



19. L. (Glossina) trentonensis Conrad. Ordovicic. 

 Oi moderate size, ovate-acute, attenuate toward the apex; sides 



nearly straight, front rounded. Surface depressed. Smooth or 

 marked by concentric lines which are crossed by obscure radiating 

 striae. 



Trenton and Utica of New York, Wisconsin, Ontario. 



20. L. rectilateralis Emmons. (Fig. 228, c.) Ordovicic. 

 Large, with nearly parallel sides, form elliptical ; front regularly 



rounded ; surface marked by radiating striae. This species is 

 readily recognized by its large size. 



Trenton-Lorraine of New York, Ottawa and Anticosti. 



