2 PALEONTOLOGY OF THE EUREKA DISTRICT. 
In the lowest fossiliferous stratum of the Cambrian in the District an 
interesting species of the genus Olenellus, O. Howelli, occurs that exhibits 
several abnormal features of development, and also certain embryonic 
characters that show the relation of the genus to the genus Paradoxides. 
Considerable space is given to the description and discussion of this species, 
and also a plate of outline figures to illustrate its variations and relations to 
other species. he specific identity of two of the three species of Olenel- 
lus, with O. Gilberti and O. Howelli from Pioche, Nevada, 130 miles distant, 
and their close resemblance to the species of Olenellus occurring in Ver- 
mont and Newfoundland, closely unites the faunas of the widely-separated 
localities, and aids materially in the correlation of the different groups form- 
ing the Cambrian system on the North American continent. 
The Lower Cambrian type of the Conocephalidz is represented by 
Ptychoparia Linnarssoni and P. Prospectensis ; and the subgeneric groups of 
the genera usually occurring in the Potsdam Group are prominent in the 
fauna of the upper portion of the Cambrian. In Protospongia fenestrata we 
have a very simple and peculiar form of silicious sponge that is probably 
identical with the Cambrian species of St. David’s, Wales. 
Much remains to be done with the small brachiopods of the Cambrian 
and Lower Silurian, since from their minute size and the imperfect state of 
preservation of the specimens collected, correct generic and specific refer- 
ences are very difficult. The one species of the genus Graptolithus in the 
upper portion of the Pogonip (Quebec) Group is the only trace discovered 
at this horizon in the Eureka District of a fauna which the writer in 1882 
found quite extensively developed in the Pinon Range to the north. The 
Graptolites from Belmont, Nevada, that were described by Dr. C. A. White 
and referred by him to the Utica slate horizon of the Trenton Group (Expl. 
and Surv. West of 100th Merid., vol. iv, part 1, p. 10), are probably from the 
horizon of the Quebec Group, or the Upper Pogonip of the Eureka section. 
The succession in the faunal series from the Olenellus (or Middle Cam- 
brian) fauna, through a large, well-defined fauna of the character of that of 
the Potsdam Group of New York and the Mississippi Valley, to one that in 
its assemblage of species combines both Cambrian and Silurian types and 
passes upward into a fauna comparable to that of the Quebec Group, or the 
