98 NEW YORK STATE MUSEUM 



half the depth of the camera ; siphuncle not retained ; living chamber rela- 

 tively very large, widening at the same rate as the septate portion ; aperture 

 not contracted, but open and simple. Surface unornamented, save by closely 

 and regularly disposed, faint growth lines, the course of which indicates the 

 presence of a shallow hyponomic sinus on the convex side of the cone. 



Locality. Lower Shelby dolomite, Oak Orchard creek. 



Observations. This large species has no equal in size among the curved 

 cephalopods of the Guelph of Canada or the Interior; it compares well in 

 this regard with the large forms to which Barrande applied the terms C. 

 tyrannus and C. rex. Cyrtoceras hercules Winch. & Marcy 

 ( = C y r t. (Phragmoceras) amplicorne Hall) is a large form from 

 the Waukesha and Racine beds of Wisconsin, which possesses a stronger 

 curvature and broader venter. Cyrtoceras bovinum, a smaller, simi- 

 larly curved species from the Guelph at Rochester, expands more rapidly 

 and has shallower camerae. Phragmoceras nestor Hall, reported 

 as from the Niagaran at Wauwatosa Wis., is readily distinguished from 

 Protoph. patronus by the constriction of its aperture, its shorter liv- 

 ing chamber and shallower camerae ; from Phragmoceras byronen- 

 sis Worthen, 1 described from the Niagaran of Port Byron 111., and which 

 very much resembles the Shelby species in the degree of its curvature and 

 rate of expansion, it differs in the same particulars. 



The form of the shell, the degree of curvature and expansion, suggest 

 relationship to Phragmoceras, as was also indicated in Hall's description 

 of C. amplicorne by addition of that generic name in parenthesis. 

 Its open aperture and slightly developed dorsoventral expansion indicate 

 that it represents one of the primitive types of the Phragmoceratidae, for 

 which Hyatt has created the genera Cordoceras and Protophragmoceras. 

 On account of the general similarity of our form with the type of the latter 

 genus, Protoph. murchisoni Barr., which makes itself obvious in 

 the curvation, expansion, situation of hyponomic sinus and ventral position 

 of sutural saddle, we refer the species thereto. 



'Geol. Sur. Illinois, 6:506. 



