250 PALEONTOLOGY OF THE EUREKA DISTRICT. 



Surface marked by strong concentric strise that curve up rather 

 abruptly in crossing the angular umbonal ridge. 



Interior characters unknown. 



There are three specimens preserving the anterior portions of the shell, 

 but none showing the entire outline. The specimen illustrated has the 

 form we have considered as belonging to the genus Sanguinolites. 



The strongly striated surface distinguishes it from described species 

 known to me. 



Formation and locality. Lower portion of Lower Carboniferous lime- 

 stone, on east slope of a small conical hill on the east side of Secret-canon- 

 road Canon, Eureka District, Nevada. 



Genus MICRODON Conrad. 



(CYPRICARDELLA Hall.) 



Microdon (Cypricardella) connatus, n. sp. 



Plate xxiv, figs. 5, 5. 



Shell transversely subovate or subrhomboidal, moderately convex. 

 Hinge-line about two-thirds the length of the shell. Beaks small, depressed, 

 and situated on the anterior third of the shell. 



Surface marked by rather distinctly defined concentric strise. 



The interior cast shows an anterior adductor muscular scar of medium 

 size, also an undefined depression extending from the beak obliquely back- 

 ward on the line of the umbonal ridge. 



Dimensions: height, 1.75 cm ; length, 3 cm ; convexity of the two valves 

 united, l cm . 



In form this species approaches very closely to Microdon ((7.) gregarius 

 Hall, and in surface characters M. (C.) bellistriatus Conrad (Pal. N. Y., vol. 

 v, pt. I ; Plates and Explanations, pis Ixxiii, Ixxiv, 1883). While differing 

 from both, it combines, in a measure, the specific characters of each. 



The reference of this and also the Devonian M.macrostriatus (ante,p. 180) 

 to the genus Microdon is tentative. Professor Hall proposed the name Eodon 

 as a substitute for Microdon, as the latter had already been used for a genus 



