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 

 l mm in thickness. 



Surface markings obscured by the exfoliation of portions of the test 

 and the adherence of the matrix; but strong, radiating striae l mm distant 

 from each other, and a few short undulations of growth, are shown on the 

 postero-lateral faces. 



Dimensions: height, 17 mm ; length, 18 mm ; breadth, 22 mm . 



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, pi. xxxi, figs. 12-14, and 

 pi. 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 striae are the same in each, as also the general form and dimensions. 



