Silurian and Devonian Fossils of Canada. 433 



'Description. — Transversely oval ; anterior and posterior extremi- 

 ties rounded ; ventral margin moderately convex, dorsal margin a 

 little more convex than the ventral ; umbones rather small, incurv- 

 ed ; greatest tumidity extending from the umbones obliquely to- 

 wards the posterior ventral angle ; surface concentrically marked 

 with fine striae and ridges of growth. Width one inch five lines ; 

 length at the centre, one inch. 



Locality and Formation. — The specimens are from an island in 

 the group lying off Point Palladeau, Lake Huron, where they were 

 found associated with Chazy, Black River and Trenton fossils ; al- 

 so at Point Claire, Island of Montreal. 



Collector — A. Murray. 



Cyrtodonta subcarinata (Billings) 



Fig. 5. 



Fi°\ 6. 



Fig. 7. 



Figure 5. A specimen from Point Claire. 

 " 6. Dorsal view of same specimen. 

 " 1. A cast from lot 26, con. 5, Osnabruck. 



Description. — Transversely sub-oval ; ventral margin scarcely 

 convex, straight or slightly sinuated for a small space of the cen- 

 tre; dorsal margin elevated in the centre and sloping with a slight 

 curve towards the posterior end, which is narrowly rounded, or 

 truncate in the casts of the interior; umbones moderately small, 

 incurved, and somewhat carinate for a greater or less distance ; 

 surface marked with obscure concentric ridges of growth. The in- 

 terior has not been seen. "Width one inch three lines ; length nine 

 lines. 



This species may perhaps be considered a variety of the last ; 

 but the proportions are somewhat different, and it is always char- 



