230 PALEONTOLOGY. 



and much wider posteriorly than on the sides, produced into spine-like 

 projections at the lateral angles. Axial lobe distinct, strongly marked, more 

 than one-third as wide as the entire shield; posterior division, or lobe, broader, 

 rounded; anterior division short; aunulation well marked ; a longitudinally 

 angular node marks the middle of the axis, extending from the anterior to 

 the posterior division, across the furrow which marks their limits. 



This species differs from the A. communis in the shorter form of the 

 cephalic shield, and proportionally longer caudal shield, both being equal in 

 this species, Avhile in that one the cephalic shield is much the longest. It 

 also differs in the wider border of the caudal shield and in the absence of a 

 node on the glabella. The caudal shield is precisely similar to that of A. 

 Josepha of the Wisconsin sandstone of similar age, except in the spine-like 

 processes of the lateral angles. The cephalic shield, however, is entirely 

 different. 



Formation and Jocaliiy. — In limestone of the Potsdam group, at Eureka, 

 Nevada. Collected by Arnold Hague, esq. 



Agnostus peolongus n. sp. 



Plate I, figs. 30-31. 



Cephalic shield elongate, or very high dome-shaped in outline; sides 

 straight, or nearly straight, for more than one-half the length, above which 

 the margin, including the anterior border, is regularly and beautifully 

 rounded. Surface low or depressed-convex in front and gradually rising to 

 near the occipital border, where it becomes low- tumid ; glabella not visible 

 except under a strong magnifying power, and by the reflection of light 

 across the surface, when the outline of a conical form, with triangular occi- 

 pital nodes, may with difficulty be detected. The shield is margined by a 

 nan-ow, somewhat rounded rim, which gradually fades out toward the 

 postero-lateral angles. Thoracic segments unknown. 



The caudal shield associated with the head is much shorter in propor- 

 tion to the width. The form is much like that of a cephalic shield, and it 

 is with some hesitation that we have associated it with the above. Its 

 shortness, however, and the want of occipital nodes, together with the 



