100 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



in the cast : fiirrow of the limb very shallow, but much more di- 

 stinct in the cast; the lower side of the border marked by distinct 

 concentric striae. 



Surface granulose; the rings of the axis minutely pnstulose. 



The larger specimens of this species measure about one inch in length. 

 It is distinguished from the P. angustifrons of the Schoharie grit by the 

 more abruptly prominent axis, the angular lateral lobes, and more prominent 

 ribs of the pygidium, as well as coarser surface-markings. 



Geological formation and locality. In the upper limestone of the Upper 

 Helderberg group : at Stafford, Batavia, and elsewhere in Genesee co. N.Y. 



PPtOETUS CRASSIMARGINATUS / 



IQ 



Calymene crassimarginata : Hall, Geol. Rep. Fourth District N.York, p. 172, f. 5. 



Proetus crassimarginatus : Hall, Corrected List of Fossils, Twelfth Annual Report 



of Regents on the State Cabinet, p. 88. 

 Phillipsia crassimarginata : Cited by Billings in the July number of the Canadian 



Journal, 1861, p. 362. 



This species is chiefly known by the numerous pygidia which occur in 

 many localities in New- York and elsewhere. The pygidium is remarkably 

 convex or hombe : it has a length and breadth sometimes nearly equal ; but, 

 when not distorted, it is wider than long. The axis is very prominent and 

 rounded ; and in good specimens, sixteen or seventeen rings may be counted, 

 and usually thirteen or fourteen. The annulations are not direct, but are 

 inclined a little forward at their origin, and, at a point about halfway up 

 the side, they bend a little backward so as to be vertical ; and again on each 

 side of the summit there is an abrupt sinuosity, and a narrowing of the ring 

 which, at the summit, is wider and direct. The sides of the axis present a 

 very peculiar appearance, as if the lateral lobes were continued into the 

 axis with the same advancing di/ection, and they terminate in acute points 

 at a little more than one-third the height of the axis ; and into the inter- 

 stices between these points the rings of the axis are inserted, making a little 

 advancing curve, and a more abrupt retral curve before reaching the summit. 

 The dorsal furrow is well defined, and the lateral lobes very convex. The 

 ribs are twelve or thirteen in number, simple, terminating in a well-marked 

 furrow ; beyond which there is a strong thickened border, which is con- 

 centrically striated on its outer margin and on the lower side. 



In the cast, the dorsal and marginal furrows are more strongly defined, 

 and the thickened border is more prominent than when the crust is preserved. 

 Surface finely granulose. 



Two fragments of the head have been observed in the same association 

 with these pygidia. One of these ( from Williams ville, the most prolific 

 locality of the species) has a very convex glabella one inch in length and 

 seven-eighths of an inch in width at the base, narrowing but little towards 



[ September, 



