216 I'ALJiONTOLOGY. 



lar surfaeo, is distinctly convex between the eye and the outer border, and 

 the hitter rather broad and flattened, separated from the inner convex area 

 by an abrupt sinus, and terminating behind in a short, sharp, rounded 

 spine, and anterioi'ly the under surface is continued in a spiniform exten- 

 sion. The facial suture starting from the front margin on a line with the 

 eye passes in a nearly direct line to the eye, behind which it passes obliquely 

 with a sigmoid curve to the posterior line of the head, a little outside of the 

 center of the movable cheek, as seen on the latter. 



Associated with the above specimens are several forms of pj-gidia, two 

 of which have the form and character of Dikelhcephalus, while other two are 

 similar to fomis associated with, and referred to heads of this kind in the 

 sandstones of Wisconsin. One of these is ti-ansversely elliptical, nearly 

 twice as wide as long, acutely pointed at the lateral angles ; the anterior 

 and posterior margins nearly equally curved, the posterior being a little 

 the most regularly arcuate. Axis narrow, and not more than two-thirds 

 the length of the shield, roundly pointed at the extremity, and marked by 

 five annulations, exclusive of the terminal ones ; lateral lobes broad and 

 flattened, very slightly convex on tha inner half; anterior border marked 

 by a comparatively strong and distinct i-ib, with two fainter, almost obsolete 

 ribs farther back ; margin wide and plain ; surface smooth. 



This species differs from any other in the collection, and also from all 

 those from the Wisconsin localities, in the general form and pustulose sur- 

 face. Mr. Billings describes a species under the name of Bathyurus conicus, 

 from the calciferous formation at St. Timothy, on the Beauharnois Canal, 

 Canada, having a similarly-formed glabella and pustulose surface, but show- 

 ing no fuiTows on the glabella. 



Formafion and JocaJlttj. — In limestone of the Potsdam group, at Eureka, 

 Nevada. Collected by Arnold Hague, esq. 



CKEnOEPHALUS (LOGANELLUS) UNISULCATUS D. sp. 

 Pluto II, figs. 22-23. 



Glabella and fixed cheeks united, elongate-quadrangular in form, the 

 entire length nearly one-third greater than the width between the suture- 

 lines on the anterior margin; sides very gently increasing in width to the 

 base of the posterior limbs. 



