394 



is sixteen lines across, and had, when perfect, about sixty marginal plates, 

 of which forty-six are preserved. 



It closely resembles both G-. Halli and Gr. Davisii, but has a larger 

 number of marginal plates, the former having thirty-six and the latter 

 about fifty. 



Locality and Formation. Rabbit Island, Lake Huron ; Hudson River 

 group. 



Collector. Prof. R. Bell. 



GASTEROPODA. 



CHITON CANADENSIS. 



Fig. 370. Fig. 371. 



Fi. 370. Chiton Canadensis. a, view of the upper side of one of the termi- 

 nal plates ; 6, side view of the same; c, underside. 

 Fig. 371. Metoptoma Montr ealensis. 



Description. The terminal plates of this species are, in form, like one- 

 half of a hollow cone with an acute apex. The anterior margin (assuming 

 this to be the posterior plate) is straight in one specimen and slightly un- 

 dulated in another, and is so convex as to form an uniform arch equal, very 

 nearly, to a semicircle. The anterior angles are narrowly rounded. The 

 upper side in one specimen has an obscure lobe along the middle, and is 

 covered with fine striae parallel to the anterior margin. Just in front of 

 the apex, on the under side, there is a thin plate, as shown in fig. a. 



Locality and Formation. Pauquette Rapids, on the River Ottawa ; 

 Black River limestone. 



Collector. E. Billings. 



METOPTOMA MONTREALENSIS. (N. sp.) 



Fig. 371. 



Description. Acutely conical ; apex a little in advance of the centre ; 

 base obtusely elliptical, the antero-posterior diameter a little the longest. 

 On a side view the outline is gently convex from the apex to the posterior, 

 and concave to the anterior margin. Surface, when perfect with fine ver- 

 tical striae running from the apex to the margin, and with both fine en- 

 girdling striae and obscure undulations of growth parallel to the base. In 

 most of the specimens the fine striae are not perceptible. 



