Silurian Fossils of Canada, 167 



spire varies greatly. A small specimen eiglit lines wide consisting 

 of three wliorls lias the spire full two lines depressed below the 

 margin the lower side being nearly flat. 



Fig. 9. Fig. 10. 



Fig 9. — Ophileta Ottawaensis. Front view partly shewing the depres- 

 sed spire. 

 10. — View of the base. The specimen figured has the whorl more 

 slender than they are in the majority of the individuals. 



In the geology of Kussia plate 23 Figs. 2a 2h De Verneuil and 

 De Keyserling have figured a species almost identical with this, 

 but they regard it as only a variety of Fleurotomaria qualteriatus. 

 It appears to me however to be a distinct species. We have in 

 the Trenton Limestone a number of species oi Pleurotomaria and 

 in some localities the individuals (although rarely perfect) are not 

 uncommon. Yet I have never seen any specimens that could be 

 considered as intermediate forms between the one here described 

 and those which belong to the group of P. qualteriatus. 



This species differs from 0. compacta Salter principally in having 

 the umbilicus concave instead of flat. 



Locality and Formation. — City of Ottawa, Trenton; not com- 

 mon. 



Collector. — E. B. 



Bellerophon Argo. (N. s.) 

 Description. — Lenticular ; from half an inch to an inch and a-half 

 in diameter, (usually about one inch) ; the dorsum with a rounded 

 edge and the sides rather strongly and uniformly convex. Whorls 

 three or four, each concealing about two-thirds of the one next 

 preceding it. Umbilicus small, exposing all the whorls in a series 

 of rectangular steps. Aperture not expanded, triangular, indented 

 on the ventral side to about one-third its height by the dorsum of 

 the penultimate whorl, the two sides gently convex uniting at 

 the dorsal angle at about 80^ or 90^. Surface apparently not 

 striated but often exhibiting some rough transverse undulations. 



