167 



Fig. 151. 



Fig. 151. — Trimerella grandis. a, cast of interior of the supposed dorsal valve ; 

 b, other side of the same cast, showing the characters of the inte- 

 rior of the ventral ? valve. 



the impressions, the ventral valve has a flat, solid, transversely-striated 

 area forming an obtuse angle with the plane of the lateral margin. Sur- 

 face of shell with obscure concentric accretion ridges. 



Length of large individual about 3 inches ; width about 2| inches. 



The casts of the interior of this species vary greatly in the length of the 

 conical projections between the septa. Although not common, they have 

 been found of all sizes from the length of 8 to 36 lines. The specimen 

 above figured is one of the various forms. It yet remains to be ascer- 

 tained how many species there may be. 



Locality and Formation. — Gait ; New Hope and Elora. In the Guelph 

 formation ; Middle Silurian. 



Collector. — J. Richardson, J. Dalgleish, R. Bell, E. Billings. 



Trimerella acuminata. (N-. sp.) 



Fig. 152.~TrimereUa acuminata. 



Remarhs. — The fragment figured below appears to belong to a distinct 

 species, difiering from T. grandis in having th„e apical extremity much 

 more pointed, and the longitudinal septa running all the way to the beak. 

 The specimen is too imperfect for description, and it is figured under the 

 above name only provisionally. It occurs with T. grandis. 



