66 PALEONTOLOGY OF THE EUEEKA DISTRICT. 



In the mode of growth and general form this species is related to E. 

 Neptuni, but differs in the details of structure. 



Several years since Dr. J. S. Newberry obtained examples of the 

 species from the White Pine Mining District, and also from Pioche, Nevada, 

 proposing the specific name E. mammilaris, in his notes, on account of 

 the appearance of the more expanded forms with the nipple-like base. An 

 illustration is given of the most abundant form in the Eureka District. 

 The complete illustration of this and its associated species of the genus is 

 deferred until sections can be prepared to exhibit the details of structure. 



Formation and localities. Upper portion of the Pogonip Group at Lone 

 Mountain, 18 miles northwest of Eureka; White Mountain, Fish Creek 

 Mountains, and Goodwin Canon in the Eureka District; and also at Pioche 

 and Treasure City, White Pine Mining District, Nevada. 



Receptaculites elongatus, n. sp. 



The general form of this species is cylindro-conical, with the central 

 depression extending deep down into the body, the thickness of the sides 

 near the base and at the summit being nearly the same. The outline of 

 the central depression is circular, and there is no evidence of the growth 

 of the sides over it as in some species of the genus from Canada and 

 Wisconsin, e. g., E. Jonesi, E. fungosum, etc. The ectorhin is formed of 

 small rhomboidal plates, arranged as in other forms of the genus ; the largest 

 plates have a greater diagonal diameter of about l mm , and a lesser one of 

 about five-sixths of l mm . The cylindrical tubes uniting the ectorhin and 

 endorhin are small, constricted at the base, and apparently smooth up to 

 their union with the plates of the endorhin. The sides of a specimen 45 mm 

 high, and with a transverse diameter of 20 mm , have a thickness of l Km above 

 and of 5 mm near the base 



This species is distinguished from any known to me by its cylindro- 

 conical form, deep central cavity, and small cells or tubes. It approaches 

 E. insularis Billings, of the Middle Silurian of the island of Anticosti (Cat. 

 Sil. Foss. Anticosti, p. 29, 1866), but differs in having the deep central de- 

 pression and a less rapidly tapering form; these features, united with the fact 



