86 PALEONTOLOGY OF THE EUKEKA DISTRICT. 



curved longitudinally ; dorsal face strongly convex and obtusely angular 

 along the center in some examples. Form of the aperture unknown. 



Surface with fine transverse striae on the ventral and dorsal sides along 

 the central portion of the tube : these were not observed towards the aper- 

 ture. 



Length of larger examples, 20 mm ; greatest width, 2.75 mm ; depth, 2 mm . 



This species is distinguished by its slender elongate form with the sub- 

 triangular section from any described form known to me. 



Formation and locality. Lower beds of the Pogonip Group, northeast 

 of Adams Hill, Eureka District, Nevada. 



CEPHALOPODA. 

 ORTHOCERATA. 



Plate xii, figs. 1, 1 a-c, 2, and 3. 



Numerous fragments of Orthoceratites occur in the upper beds of the 

 Pogonip Group at Lone Mountain and the Fish Creek Mountains. From 

 among them several well-defined species may be selected. 



1. Endoceras proteiforme Hall? (Pal. N. Y., vol. i,p. 208, 1847) ; plate xii, figs. 1,1 o-c. 



This is the most abundant, and is found at the principal exposures of 

 the upper portion of the group, and the transverse sections (fig. la) are 

 often seen. In fig. 1 the siphuncle with an inner tube is shown, and fig. 

 1 c shows the annulations on the outer surface of the siphuncle. 



2. Orthoceras multicameratum Hall? (Pal. N. Y., vol. i, p. 45, 1847); plate xii, tig. 3. 



The fragment illustrated on plate xii, fig. 3, and also several not figured, 

 shows a form closely allied to the species from the Birdseye limestone of 

 New York; with the exception of the tube not converging as rapidly to- 

 wards the apex the specific resemblance is very strong. 



3. Orthoceras sp. ? plate xii, fig. 2. 



An elongate form of the type of the preceding species. The material 

 representing it is so fragmentary that a specific identification is not at- 

 tempted. 



