24 PALEONTOLOGY OF THE EUEEKA DISTEICT. 



There appears to be very little difference between the Eureka speci- 

 mens and those described by Professor Hall from the Potsdam sandstone 

 of Wisconsin. Dr. C. A. White describes similar forms from Pioche, Nevada, 

 where they occur in strata of ("Primordial") Cambrian age. 



Formation and localities. Cambrian. Prospect Mountain Group, in 

 the upper beds of the Secret Canon shale, on the east side of New York 

 and Secret Canons, and on the east side of the canon at the eastern side of 

 Euby Hill. Also in an outcrop of limestone on the west side of the foot- 

 hills of Combs' Peak, Antelope Valley, Eureka District, Nevada. 



PCECILOPODA. 

 Genus AGNOSTUS Brongniart. 



Agnostus Richmondensis, n. sp. 

 Plate is, fig. 10. 



Cephalic shield moderately convex, length and breadth equal, sides 

 scarcely parallel, rounding in front into the broadly rounded anterior 

 margin. Glabella three-fourths the length and a little more than one-third 

 as wide at the base as the width of the shield, it is elongate-conical in out- 

 line, strongly denned by the dorsal furrows, and with the anterior third 

 separated by a distinct transverse furrow, a little less than midway between 

 this furrow and the posterior margin a short furrow penetrates from each 

 side towards the base of a minute tubercle situated on the median line, 

 two oblique furrows cut off the posterior lateral angles as two small rounded, 

 triangular node.s; lateral lobes more convex than the glabella, divided 

 anteriorly by a slight median furrow, surrounded by a narrow, rim-like 

 margin, and ornamented by slightly irregular depressed lines that indent 

 the surface from the margin nearly to the edge of the strong dorsal furrows. 



Surface smooth under an ordinary magnifying power. 



Dimensions. Length and breadth, 2.5 mm ; depth of shield, O.TS 11 . Tho- 

 racic segments and caudal shield unknown. 



