66 PALEONTOLOGY OF THE EUREKA DISTRICT. 
In the mode of growth and general form this species is related to R. 
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 &. 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., R. Jonesi, R. 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 1™", and a lesser one of 
about five-sixths of 1™™. 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™ 
high, and with a transverse diameter of 20", have a thickness of 7™™ above 
and of 5™™ 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 
R. 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 
