88 NEW YORK STATE MUSEUM 



Cyrtoceras erodes Billings 



Plate 15, fig. 3-n 



Cyrtoceras orodes Billings, Paleozoic Fossils. 1865. i : 162 (not figured) 

 Cyrtoceras orodes Whiteaves, Paleozoic Fossils. 1895. v. 3, pt 2, p. 103, pi. 14, 



fig- 7-9 



Several specimens of this species presenting a very slightly curved and 

 rapidly tapering shell with nearly circular section, have been obtained from 

 the lower Shelby horizon and at Rochester. The original, which was not 

 figured by Billings, and two specimens of better preservation have been 

 described and figured by Whiteaves. 



The New York specimens are of moderate size, tapering rapidly (one 

 increasing from n to 19 mm in 39 mm; another from 12 to 28 mm in 60 

 mm), very gently curved, of nearly circular section, becoming somewhat 

 flattened dorsoventrally in late growth. Billings describes the dorsoventral 

 diameter as being slightly the greater, which is true of earlier growth, while 

 the outline of the section of the type specimens given by Whiteaves is cir- 

 cular. The septa are closely arranged; in the smallest specimens from 1.5 

 mm apart at the smaller end to 4.5 mm at the larger. The septa are but 

 slightly concave, their depth being no more than 2 mm. The sutures run 

 nearly straight across the shell ; they show a very short, blunt lobe over the 

 siphuncle on the ventral surface, and a very faint, broad lobe over the dor- 

 sal surface. The siphuncle is situated close to the ventral side and is not 

 expanded between the septa. 



The surface appears to have been smooth, the inner shell larger and, 

 as shown in one specimen, bearing some fine, longitudinal furrows. 



The species has not been collected in the upper Guelph of Oak Orchard 

 creek, while in the lower bed both young and adult specimens were found, 

 the former exhibiting well the rather rapid expansion of the conch, and the 

 latter retaining part of the living chamber and a number of the youngest 

 camerae. In a large example the living chamber becomes greatly con- 

 tracted toward the aperture in about the same degree as a specimen 



