116 PALEONTOLOGY OF THE EUEEKA DISTKICT. 



of the New York examples, but their specific identity is unquestionable. 

 The specimens from the lower horizon at Lone Mountain are preserved in a 

 different matrix and the outer surface is mostly exfoliated, which gives 

 them a dissimilar appearance, but no specific variation can be determined 

 between them and those from the upper horizon at The Gate. 



formation and localities. Devonian limestone, higher beds at The Gate, 

 northwest of Eureka, and lower beds at Lone Mountain, 18 miles northwest 

 of Eureka, Nevada. 



Genus SKENIDIUM Hall. 



Skenidium Devonicum, u. sp. 

 Plate xiii, lig.s. 4, 4n. 



Shell small, subpyramidal ; hinge line a trifle shorter than the greatest 

 width of the shell; a sharp, median fold marks the ventral valve and a 

 .slight sinus the dorsal. Ventral valve elevated, beak slightly incurved over 

 a high area that is divided midway by a large deltoidal foramen. Dorsal 

 valve nearly flat; area very short; foramen short and broad; cardinal pro- 

 cess extends as a median septum towards the lower portion of the valve. 



Surface marked by strong radiating striae that increase by implanta- 

 tion. 



Dimensions: length, 3.5 mm ; breadth, 4.. r ) mni ; elevation of ventral valve, 

 1 .5 mra . 



This species has a less elevated area, finer and sharper striae than Ske- 

 itidiHiH insignis-=z(Ortliis insiynis Hall, Pal. N. Y., vol. iii, p. 173, pi. xiii, figs. 

 1, ">-!;"), 1859) of the Lower Helderberg limestone of New York; otherwise 

 the two strongly resemble each other. 



This is the first time that the genus Skenidium has been reported as 

 occurring in Devonian strata, the species previously referred to it coming 

 from the Lower and Upper Silurian formations. 



Formation and locality. Devonian limestone, lower horizon, Lone 

 Mountain, 18 miles northwest of Eureka, Nevada. 



