64 PALEONTOLOGY OF THE EUREKA DISTEICT. 



almost tumid on the frontal lobe, and in compressed examples slightly 

 projecting over the anterior margin; marked by three pairs of oblique, 

 slightly impressed furrows; these are united across the center by short 

 transverse depressions; occipital furrow shallow; occipital ring strong, 

 flattened; fixed cheeks of medium width, separated from the glabella by 

 distinct but lightly impressed dorsal furrows, and sloping outward to the 

 medium-sized eyelobes; postero-lateral limbs strong and well extended 

 laterally; frontal limb as a narrow margin close to the front of the glabella. 



The facial sutures have the general course of those in the genera 

 Ogygia and Asaphus. 



The above description is drawn from a well-preserved adult specimen 

 of the head, that, excepting the free cheeks, is 23 mm in length. In a young 

 example of the same parts, 7 mm in length, the glabella is less convex, 

 subangular in front, sloping to the margin, and the glabellar furrows are 

 obsolete; in other respects it strongly resembles the adult. 



With these parts before us we would refer the species to Ogygia; but 

 in every instance where they have been found there are pygidise, tho- 

 racic segments and fragments associated with them that indicate an entirely 

 different genus. An illustration is given of the pygidium on plate x, fig. 

 2 a, and of the segment, fig. 2b. They occur in association along an out- 

 crop of several miles, and no other species of a similar size is known to 

 exist at the same horizon. No genus known to us combines the characters 

 presented by the head and pygidium, and, although they have not been 

 seen united to the thorax, the evidence is in favor of their belonging to 

 the same species. 



A provisional reference is made to Ogygia, the genus to which the 

 head appears to belong, the pygidium and thoracic segments having more 

 the character of those referred to Dicellocephalus. 



Formation and localities. Cambrian. Prospect Mountain Group, upper 

 beds of the Secret Canon shale, on the east side of Secret and New York 

 Canons, and on the south slope of Adams Hill, Eureka District, Nevada. 



