FOSSILS OF THE DEVONIAN. 121 



from the Upper Helderberg through the Hamilton and into the Chemung 

 Group. Its geographic range also includes the Province of Ontario, Can- 

 ada, and the States of Illinois and Iowa. 



Formation and localities. Devonian limestone, Comb's Peak and Newark 

 Mountain, Eureka District; Lone Mountain, 18 miles northwest of Eureka,. 

 Nevada. 



Strophodonta punctulifera Conrad (sp.) 

 Plate xiii, fig. 10. 



For list of synonyms and remarks, see Paleontology of New York, vol. iii, p. 188; 

 vol. iv, p. 95 ; Pal. Province of Ontario, p. 68. 



This species has usually been considered a Lower Helderberg form, 

 although, as stated by Professor Hall, Mr. Billings, and Professor Nicholson, 

 it is closely allied to, if not identical with S. ampla, of the Upper Helder- 

 berg and Hamilton Groups. The Nevada specimens show a convex dorsal 

 valve, slightly concave about the umbo, with strong radiating striae and: 

 punctate surface, the latter showing where the surface is covered with fine 

 concentric striae. The Nevada shell is not referable to S. ampla, as found 

 in New York, and as it approaches S. punctulifera very closely the reference 

 is made to that species. . 



Formation and locality. Lower horizon of the Devonian limestone,. 

 Lone Mountain, 18 miles northwest of Eureka, Nevada. 



Strophodonta arcuata Hall ? 



Strophodonta arcuata Hall, 1858. Geol. of Iowa, vol. i, pt. 2, p. 492, pi. iii, figs. Ia-c 



2 a, 6, e, f. 

 Calvin, 1878. Bull. U. S. Geol. Survey, vol. iv, p. 728. 



A comparison with specimens from Rockford, Iowa shows the Nevada 

 shell to be less convex than the average examples, but not less so than some. 

 It agrees otherwise in nearly every particular. 



Formation and locality. Devonian limestone, south spur of Atrypa Peak,, 

 Eureka District, Nevada. 



