2 PALEONTOLOGY OF THE EUREKA DISTRICT. 



In the lowest fossiliferous stratum of the Cambrian in the District an 

 interesting species of the genus Olenellus, 0. 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. The specific identity of two of the three species of Olenel- 

 lus, with 0. 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 con-elation of the different groups form- 

 ing the Cambrian system on the North American continent. 



The Lower Cambrian type of the Conocephalidse is represented by 

 Ptyclioparia 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 Pifion 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 1 00th 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 



