39 



front in the middle, the anterior slope gently concave or nearly straight 

 and the posterior gently convex. The posterior part of the shell is a little 

 compressed and there is a wide shallow concave depression running from 

 the apex to the base near the posterior edge. Surface unknown. Height 

 about 1 inch, length of base 11 lines, greatest width 7 lines. 



Fig. 40. Fig. 41. 



Fig. 40. Metoptoma Orithyia. a, form of the base; 6, side view. 

 41. M. Trentonensis. a, view of the upper side ; 6, side view. 



Locality and Formation. Phillipsburgh, in the County of Missisquoi, 

 Canada East. In the upper part of the Calciferous formation. 

 Collector. E. Billings. 



METOPTOMA ERATO. (N. sp.) 



Description. Elongate, oval, posterior margin uniformly rounded ; sides 

 very gently convex : anterior extremity narrowly rounded or pointed, form- 

 ing an angle of about 90. The shell for the greater part is uniformly 

 convex ; on approaching the apex compressed at the sides, forming 

 a narrowly rounded or subcarinate umbo. The greatest elevation 

 is in the anterior half of the shell ; the apex is obtusely pointed and 

 depressed so that its position is at about half the whole height of the 

 shell. The outline in a side view gently concave at the anterior extremity 

 beneath the apex, while above it is uniformly curved from the apex to 

 the posterior margin. Surface nearly smooth but shewing indications of 

 concentric striae. 



Length 11 lines ; width 7 lines ; height 3 lines. 



Of this species I have seen only three specimens. Two of these seem 

 to be slightly unsymmetrical or have the apex not quite in the median line. 

 It is closely allied to M. Nycteis, but is smaller and more depressed. 



Locality and Formation. Paquette Rapids, on the Ottawa River. 

 Black River limestone. 



Collector. E. Billings. 



