FOSSILS OF THE DEVONIAN. 135 



by Mr. Meek were small, but do not differ from specimens of the same size 

 found at Newark Mountain or specifically from the larger shells that are 

 identical with examples of the species found in New York and also in Eng- 

 land. 



Formation and localities. Central and upper portions of the Devonian 

 limestone, Newark Mountain, and at The Gate, northwest of Eureka, Ne- 

 vada. 



Spirifera raricosta Conrad (Sp.). 

 Plate iv, figs. 2, 2 a; pi. xiv, fig. 12. 



Delthyris raricosta Conrad, 1842. Jour. Acad. Nat. Sci. Philad., vol. viii, p. 262, pi. 



xiv, fig. 18 



undulatm Vanuxein, 1842. Geol. Eep. Third District New York, p. 132, fig. 3. 

 Spirifera raricosta Billings, 18C1. Can. Jour., vol. vi, p. 258, figs. 71-73 of p. 259; Pal. 



Fossils, 1874, vol. ii, pt. 1, p. 47, pi. 3 A, figs. 5, 5 a, b. 

 Hall, 1867. Pal. New York, vol. iv, p. 192, pi. xxvii, figs. 30-34, pi. 



xxx, figs. 1-9. 

 Nicholson, 1873. Pal. Prov. Ontario, p. 82. 



A species closely allied to this, if not identical, occurs in the lower 

 fossiliferous horizon of the Devonian limestone. It differs in not having 

 quite as distinct concentric strise, and also in the absence of the prominent 

 septum shown in casts of the ventral valve of specimens from the Schoharie 

 grit of New York. These are characters that are variable in the New York 

 forms, and do not afford data for the establishment of a distinct species on 

 the examples thus far obtained in Nevada. 



At the East this species ranges through the Schoharie grit and Cor- 

 niferous limestone of the Upper Helderberg Group, and its known geo- 

 graphical extension carries it west from New York across the State of Ohio 

 to Southern Indiana and northwest into Canada West. 



A larger series of specimens from Lone Mountain, collected a year 

 after the above was written, show a gradation in form from Spirifera rari- 

 costa to S. duodenaria, the constant differences in the median sinus and fold 

 alone serving to distinguish, in external characters, the two species. 



Formation and localities. Lower horizon of the Devonian limestone, 

 Comb's Peak, Eureka District, and Lone Mountain, 18 miles northwest of 

 Eureka, Nevada. 



