114 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Formation and locality—lLower Devonian of Brush Peak, Eureka Dis- 
trict, and at the same horizon at Lone Mountain, 18 miles northwest of 
Eureka, Nevada. 
Pholidops quadrangularis, n. sp. 
Plate ii, fig. 7. 
Shell broadly oval, or subquadrangular; moderately elevated. Sides 
nearly straight, which gives the quadrangular outline to the shell. Apex 
eccentric and a little elongate. Slope from the apex to the margin uniform. 
Surface marked by irregular, not very prominent lamellose striz. Substance 
of shell calcareous. Dimensions: Breadth, 5.5™"; length, about 6.5™™. 
This species is unlike any described form known to us, and although 
only represented by a single valve showing the exterior, it is too well marked 
to be confused with any species from the Eastern United States. 
Formation and locality—Lower Devonian at Lone Mountain, 18 miles 
northwest of Eureka, Nevada. 
Genus ORTHIS Dalman. 
Orthis McFarlanei Meek. 
Orthis Mc. Farlanei Meek, 1868. Trans. Chicago Acad. Sci., vol. i, p.88, pl. xii, figs. 1a—-h. 
This large species is so strongly marked by its peculiar form that the 
identification is rendered very satisfactory, although based on imperfect 
specimens. Its short hinge line, great convexity of the dorsal valve, and 
narrow umbonal region give it the appearance of Pentamerus galeatus, as 
mentioned by Meek. The Nevada specimens show the fine radiating strize 
and minutely punctate surface with great distinctness, as in the original types 
of the species from the Mackenzie River Basin, British America. Mr. Meek 
states that he had seen specimens which he believed to be identical with 
this species from the Devonian of Iowa and Illinois. 
Formation and locality—Lower horizon of the Devonian limestone, west 
slope of County Peak, Eureka District, Nevada. 
