40 



Metoptoma Trentonensis. (N. sp.) 



Fig. 41. 



Description. — Shell small, nearly circular, anterior margin obtusely- 

 rounded or subtruncate ; convex most olovatod a little in advance of the 

 middle. The apex varies somewhat in its position. In some specimens 

 it is directly over the anterior margin, and in such it is depressed below 

 the greatest elevation of the shell. In others it is a little beliind the 

 anterior margin or nearly central, in which cases it sometimes forms the 

 most elevated point. The shell is thick and the surface marked with fine 

 striae and often with irregular tumid ridges of growth. The form in some 

 is perfectly circular but in others the anterior margin is nearly straight 

 beneath the apex, or very gently rounded showing an approach to the 

 regularly truncated species. The individuals vary little in size being in 

 general Ti or li lines in length and breadth and 2 or 3 Hues in height. 



This species is more abundant in individuals than any other known in 

 our rocks but apparently confined to particular localities. 



Localitii and Formation. — Chevroti^re and Island of Montreal. Trenton 

 limestone. 



Colleclurs. — Sir W. E. Logan, J. Richardson. 



AvicuLA Heemione. (N. sp.) 



Fig. 42. 

 Fig. 42. — ivicula Hermione. 



Dm'rijit ion.— Ovutd, front margin broadly rounded, convex, most pro- 

 mment in the upper half. Beaks small, closely incurved, umbo narrowly 

 convex but not so much elevated as the middle of the shell. Hinge line 

 and wmgs miknown. Surface ornamented with strong concentric strise 



