GUELPH FAUNA IN THE STATE OF NEW YORK 91 



being only 3.5 mm apart, where the major diameter of the conch is 43 

 mm ; deeply concave, the deepest place dorsad of the center, bent forward 

 strongly in the ventral and slightly in the dorsal region. Depth of septum 

 of living chamber 8 mm ; sutures transverse, with a higher, but narrow, 

 rather sharp ventral, and lower, broader dorsal saddle, straight on the 

 sides ; transverse section oval, compressed laterally, the venter narrower 

 than the dorsum, major and minor diameters in one narrow specimen 39 

 and 30 mm, in another broader, 44 and 36 respectively ; siphuncle small, 

 4.5 mm wide at the perforation of the septum, where the latter has a major 

 diameter of 44 mm, apparently empty, expanding to its double diameter in 

 the camerae, situated propioventran ; living chamber short, retaining the 

 curvature and expansion of the septate portion, aperture not constricted, 

 its lateral margins low, convex, the dorsal margin provided with a broad 

 and lower sinus and the ventral margin with a narrower and somewhat 

 deeper hyponomic sinus situated on the arched external side (exogastric 

 shell) ; surface not known, the internal casts being smooth and the molds 

 of the external surface obscured by coating of crystals. A coarse orna- 

 mentation was evidently absent. 



Locality. Lower Shelby dolomite. 



Observations. From Cyrtoceras cancellatum Hall, the only 

 form of the New York Niagaran showing some superficial similarity, C yrt. 

 curvicameratum is readily distinguished by being laterally com- 

 pressed and not dorsoventrally as the latter. In the rich cephalopod fauna 

 which has become known from the western Niagaran, there are Cyrt. 

 fosteri Hall and Cyrt. dardanus Hall, both clearly related to this 

 species. Cyrtoceras fosteri Hall, described 1 from the "Niagara 

 limestone" near Chicago, possesses a similar transverse section, curvature 

 of sutures and like depth of chambers, but differs in having the venter 

 relatively narrower and the ventral saddle of the sutures higher. Cyr- 

 toceras dardanus Hall, occurring in the Racine beds at Waukesha 

 and Wauwatosa Wis., a form with similar curvature and expansion, is 



1 Report of Progress of Geological Survey of Wisconsin for i860, p. 41. 



