4 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Lower Trenton and indicating an horizon that is considered to be in a 
measure the equivalent of that of the Chazy formation of New York and 
Canada. The fauna of the lower portion of the Pogonip Group corre- 
sponds in the same manner to that of the Calciferous sand-rock of the same 
region. The large number of individuals of the species of Receptaculites, 
R. mammillaris especially, gives the fauna of the upper beds a character 
that this horizon has not hitherto had. This, united with several of the 
Trenton species, viz, Orthis testudinaria, O. tricenaria, O. perveta, Tellinomya 
contracta, two species of Modiolopsis allied to Trenton forms, and Raphis- 
toma Nasoni, strongly foreshadows the opening of the Trenton period. 
The fauna between that of the Pogonip and the Devonian horizon is 
so meager that the only reference made to it is in the systematic list and in 
the lists of the geologic report (Geology of the Eureka District). As the 
determination of a higher Silurian horizon than that of the Trenton-like ~ 
fauna in the limestone above the quartzite capping the Pogonip Group 
rested mainly on the presence of the genus Halysites, the opinion of Prof. 
James Hall was requested as to the generic relations of the specimens that 
had been referred to Halysites in the field. While he did not say positively 
that the form represented was Halysites, he expressed the opinion that it 
was of organic origin, and that he knew of nothing else but Halysites to 
which it could be referred. This conclusion has since been fully proven by 
the discovery of fine specimens of Halysites catenulatus at the same horizon 
in the White Pine District, Nevada, associated with specimens in a similar 
state of preservation as those from Lone Mountain. 
The fauna of the Devonian is large and representative, notwithstand- 
ing some speciés have reversed their relative position in the group as they 
have been known heretofore, and othersshave a greater vertical range. 
Among the brachiopods, Orthis Tulliensis, of the Tully limestone of New 
York State, is found at the summit of the Devonian limestone, and Orthis 
impressa, 1 Chemung species of New York, at the base, associated with 
eastern Upper Helderberg limestone species; and a variety of Atrypa reti- 
cularis, characteristic of the Niagara limestone, and unknown heretofore 
elsewhere, occurs with the former in the upper beds. Among the corals, 
Cladopora pulchra, Syringopora Hisingeri, and Cyathophyllum corniculum, of 
