224 rAL.T:ONTOLOGY. 



each side of the middle. Ghibella strongly convex, subangiilar along the 

 central line ; broadly conical in outline, and rounded-truncate in front ; the 

 length from the occipital furrow a very little exceeding the greatest width 

 at base ; marked by two i)airs of transverse furrows, which divide it into 

 three nearly equal parts on the margin, and are directed very obliquely 

 backward for their entire length, reaching two- thirds of the distance between 

 the margin and the median line. Occipital furrows broad, well detined ; 

 occipital ring rather strong. 



Fixed cheek wide, separated from the glabella by an indistinctly 

 defined furrow; ocular ridge strong, rising from the upper lateral angles 

 of the glabella, and passing with but little curvature to the anterior angle of 

 the eye. Front border of the head of moderate width ; marginal rim thick- 

 ened and cord-like, separated from the inner portion by a deeply-marked 

 furrow, within which the surface rises abruptly to the edge of the narrow 

 anterior furrow bordering the glabella. Posterior lateral limbs unknown. 



Surface of the fixed cheeks and frontal limb marked with strong, scat- 

 tered granules or pustules. The surface of the glabella may have been 

 marked with similar pustules, but has been somewhat injuixnl by Aveather- 

 ing, so that none show in its present condition. 



The species somewhat closely resembles Ptychaspis Miniscaensis Owen's 

 sp., from the Mississippi Valley, in the forai of the glabella and the furroAvs 

 marking the same, but diff"ers in the Avider fixed cheeks and the form of the 

 anterior border, so far as that one is known, as well as in the pustulose 

 surface. No other parts of the organism have been detected than those 

 here described. 



Formation and locuUtij. — In the lowest layers of limestone seen, on the 

 Avest side of Pogonip Mountain, White Pine District, Nevada; of the age 

 of the Potsdam sandstone. Collected by Arnold Hague, esq. 



Genus CIIARIOCEPHALUS Hall. 



ClIAKlOCEPHALUS TUMIFRONS U. Sp. 

 Plato II, fias. 38-39. 



Glabella large, prominent, and cylindrical, nearly as Avide as long, 

 strongly rounded and protuberant in front, projecting beyond the rim of the 



