32 CANADIAN FOSSILS. 



Indeed it is much to be wished that a name so ill applied as 

 Gyroceras should be abolished altogether. Originally given by 

 Meyer to the Spirula comprcssa of Von Buch, which has since proved 

 to be a Goniatites, M. d'Orbigny had no warrant for applying the 

 name to a totally different form. And as the position of the siphon 

 will not distinguish the two genera, there remains but the somewhat 

 obscure character of its more solid radiated structure to separate the 

 two genera. It would be better to reunite them, and when the 

 value of this character is better known, to complete the classification. 



We are fortunately able to present two extreme forms of the genus 

 in one plate : the one smooth on the surface and much laterally 

 compressed, as in the several Silurian forms ; the other ornamented 

 with large, frill-like varices of growth, and with a wide section, like 

 those of the Devonian species. Some of these latter (referred to 

 Cyrtoceras by Goldfuss and Phillips,) are as much involute as a 

 Lituites, and are wide in section, the fore and aft diameter, so to 

 speak, being less than the tranverse measure. 



Cyrtoceras falx. 



Decade I. Plate VII. Figure 1-4. 



Synonym. — C.falx, Billings. Report of Progress, Geological Survey 

 of Canada, 1857, p. 314. 



A smooth shell, or with very faint and nearly direct lines of 

 growth. It is strongly curved, and somewhat compressed, about 

 two inches long, rapidly tapering from ten lines broad to two and 

 a half, and in some specimens more quickly. Aperture oval, ten 

 lines broad by eight thick. Siphon nearly close to the peripheral 

 margin. Septa close, concave from back to front. 



I have Mr. Billings' own authority for identifying this shell with the 

 species described by him, else I should have regarded it as rather 

 belonging to the other allied species (from the same locality) which 

 he has termed C. simplex. As the specimen figured — and others 

 stilL more perfect — are in the Canadian Museum — I beg to refer to 

 his description in the Report of Progress of the Geological Survey, 

 published 1S57, pp. 313, 314,) for the specific characters. It might 

 be compared with C. macrostomum, C. arcuatum, and C. camurum, HalU 

 but all have more distant septa. 



Locality. — Pauquette's Rapids. 



