FOSSILS OF THE POTSDAM GKOUP. 225 



head fully one-fourth of its entire length, including the occipital ring, in a 

 rounded, tumid boss ; marked by two transverse furrows anterior to the 

 occipital ring, the anterior one rudimentary and dii'ected forward, visible 

 only on the sides of the glabella ; posterior furrows strong and deep, but nar- 

 row, extending entirely across the glabella in equal strength and nearly in 

 a direct line, situated a little in front of the middle of the entire length of 

 the head; occipital furrow a little stronger than the posterior glabellar 

 furrow, directed slightly forward in the middle. Occipital ring wide and 

 flattened, about of the same dimensions as the space between the occipital 

 furrow and the posterior glabellar furrow. 



Fixed cheeks trapezoidal, strong, and broad, inflated and tumid between 

 the eye and the glabella, so as to overhang the eye and the suture-line. 

 Frontal limb very short, and abruptly bent downward. Posterior lateral 

 limbs short-triangular, nearly vertical outside of the line of the eye ; 

 occipital furrow deep, and the ring narrow; ocular sinus very small, situ- 

 ated on a line with the occipital furrow of the glabella. 



Facial suture cutting the anterior margin of the head a little outside 

 of the line of the glabella, and almost immediately deflected outward with 

 a strong convex curvature to the ocular sinus, behind which it is dii'ected 

 to the posterior border at an angle of about forty-five degrees to the axis. 



Surface of the crust smooth, so far as can be determined from the 

 specimens. 



The species will be easily recognized by the highly convex and cylin- 

 drical glabella, which projects far in advance of the frontal border of the 

 head. 



Formation and locality. — In the lowest limestone beds on the west side 

 of Pogonip Mountain, White Pine District, Nevada, of the age of the Pots- 

 dam group ; associated with Conocephalites {BiJcellocephalus) laticeps, JBathy- 

 urus f angulatus, &c. Collected by Arnold Hague, esq. 



Genus DIKELLOCEPHALUS Owen. 



Associated with the preceding species from the Eureka beds of the 

 Potsdam group are two forms of pygidia, so unlike anything positively 

 known to belong to species with conical or slipper-shaped glabellas, that it 



15 P E 



