196 PALEONTOLOGY OF THE EUREKA DISTRICT. 
terminating within the margin; the slope from the apex is very slightly 
convex; height a little less than the postero-anterior diameter; test about 
1”™™ in thickness. 
Surface markings obscured by the exfoliation of portions of the test 
and the adherence of the matrix; but strong, radiating strize 1™ distant 
from each other, and a few short undulations of growth, are shown on the 
postero-lateral faces. 
Dimensions: height, 17"™; length, 18""; breadth, 22™™. 
Formation and locality—Lower horizon of the Devonian limestone; west 
side County Peak, Eureka District, Nevada. 
PTEROPODA. 
Genus TENTACULITES Schlotheim. 
Of the four species of the genus Tentaculites now known to occur in 
the lower horizon of the Devonian limestone, three appear to be specifically 
identical with well-recognized species of the Lower Devonian of the State 
of New York, while the remaining form is distinguished only by the surface 
characters, which are often unreliable owing to the imperfect preservation 
of the test. This is illustrated by Tentaculites gracilistriatus, where, on the 
same block of limestone, specimens occur preserving the annulations and 
fine striae, and others on which it is exceedingly difficult to determine either 
The species are identified by comparisons with specimens from New 
York, and also with the beautiful illustrations and careful descriptions in the 
Paleontology of New York (vol. v, part 2). 
Tentaculites gracilistriatus Hall (Pal. N. Y., vol. v, pt. 2, p. 173, pl. xxxi, figs. 12-14, and 
pl. xxxi A, figs. 37-47). 
This neat and strongly defined species occurs in the greatest numbers 
and is the most widely distributed of the forms found in the Eureka Dis- 
trict. It posesses all the characters given it by its author in describing the 
New York types; the variation in the form and prominence of the annula- 
tions, the solid apical portion devoid of annulations, and the crowded longi- 
tudinal striz are the same in each, as also the general form and dimensions. 
