FOSSILS OF THE CAMBRIAN. 



27 



Dimensions of cephalic shield. Length, 3.25 mm ; width, 3.75 mm ; caudal 

 shield as 4 is to 5 in length and breadth respectively. 



A comparison of specimens made after the manuscript of this report 

 was written shows that the supposed new species of Agnostus is identical 

 with Mr. Meek's A. Widens from the Gallatin River, Montana, also that 

 Ptycnoparia Gallatinensis occurs in association with it in Montana and 

 Nevada. 



Formation and localities. Cambrian. Prospect Mountain Group ; 

 ranges from the upper portion of the massive Prospect Mountain lime- 

 stone as found in the 700-foot level of the Richmond mine at Ruby Hill 

 and on the east slope of Prospect Mountain, to the summit of the Ham- 

 burg limestone, near the Hamburg mine, and into the base of the Po- 

 gonip Group, occurring most abundantly in the upper beds of the Secret 

 Canon shale, Eureka District, Nevada. Also in the Lower Pogonip Group 

 on Pogonip Ridge, White Pine District, Nevada. 



Agnostus commtmia H. & W. 



Agnostus communis Hall & Whitfield, 1877. Geol. Expl. Fortieth Parallel, vol. iv, 

 p. 228, pi. i, figs. 28 and 29. 



This species has a vertical range similar to the preceding, and occurs 

 at the same localities, although rarely in the same layer of rock. The orig- 

 inal specimens were collected by the geologists of the Fortieth Parallel 

 Survey from the White Pine Mining District, Nevada. 



Agnostus Neon H. & W. 



Agnostus Neon Hall & Whitfiekl, 1877. Geol. Expl. Fortieth Parallel, vol. iv, p. 229, 

 pi. i, figs. 26, 27. 



Associated with Agnostus communis, and. having essentially the same 

 range and distribution in the district, the original types coming from the 

 Eureka District, Nevada, by the same survey. 



