FOSSILS OF THE DEVONIAN. 



169 



As far as can be determined by a comparison of the single right valve 

 that we have of this species with specimens, and also Professor Hall's figures, 

 it is identical with the New York species. It occurs in association with the 

 following Chemung species : Orthis impressa, Productus speciosus, P. lacliry- 

 mosa, vars. lima and stigmata, Spirifera disjuncta, Atliyris Angelica, Ehyncho- 

 nella sinuata, Sanguinolites rigidus. 



Formation and locality. -r-Upper Devonian, at The Gate, northwest of 

 Eureka, Nevada. 



Subgenus PLETIIOMYTILTTS Hall. 



Mytilarca (Pie thorny tilns) oviformis Conrad. 

 Plate v, fig. 11. 



Inoceramus oviformis Conrad, 1842. Jour. Acad. Nat. Sci., Philad., vol. viii, p. 246, 



pi. xiii, fig. 7. 



Mytilarca oviformis Hall, 1870. Prelim. Notice Lam.. Shells, p. 21. 

 Plethomytilus oviformis Hall, 1883. Pal. N. Y., vol. v, pt. 1; Plates and Explanations, 



p. 11; pi. xxxi, figs. 1-8. 

 Mytilarca (Plethomytilus) oviformis Hall, 1884. Pal. N. Y., vol. v, pt. 1, p. 255; pL 



Ixxxvii, fig. 8. 



But a single left valve of this species has been obtained. In form and 

 external characters it corresponds too closely with M. (P.) oviformis of the 

 Hamilton Group of New York to admit of a specific separation. It may be 

 that if the ligamental area and hinge were known, differences of generic 

 value would appear, but with the present knowledge of the shell this is not 

 anticipated. 



Formation and locality. Lower Devonian, Lone Mountain, 18 miles 

 northwest of Eureka, Nevada. 



Genus MODIOMOEPHA Hall. 



Modiomorpha altiforme, n. sp. 

 Plate v, fig. 9. 



Shell transverse, suboval to subquadrangular in outline. General sur- 

 face strongly convex, with the umbonal ridge prominent. 



