FOSSILS OF THE DEVONIAN. 



149 



Athyris Clara Billings, 1860. Canadian Journal, vol. v, p. 274, figs. 29-32. Ibid., 1863. 



Geology of Canada, p. 373. figs. 397 a, b. 



Meristella nasuta Hall, 1867. Pal. N. Y., vol. iv, p. 299, pi. xlviii, figs. 1-25. 

 Athyris nasuta Nicholson, 1874. Pal. Prov. Ontario, p. 86. 

 Compare Whitfieldia tumida Dalman's (Sp.). 



Professor Hall (Pal. N. Y., vol. iv, p. 299) cites Atrypa nasuta Conrad 

 Ann. Report on the Paleontology of New York, p. 18. I have not been 

 able to find any such reference, but find the original description in the 

 Journal of the Philadelphia Academy of Natural Sciences, as cited above. 



A number of examples of this species occur at the Lower Devonian 

 horizon of Lone Mountain, in association with other well-known Upper 

 Helderberg or Corniferous limestone fossils of the eastern side of the conti- 

 nent. None of them attain the large size of many specimens from New 

 York and Canada, but their specific identity with specimens of a corre- 

 sponding size scarcely permits of question. The presence of a narrow 

 depressed line or median sinus on both valves is a character absent on Jf. 

 nasuta, but present in the closely allied Whitfieldia tumida Dalman (sp.) 

 (Davidson, 1882, Mon. Brit. Foss. Brach., vol. v, p. 107) of the Upper 

 Silurian. The broader depressed fold of the dorsal valve and rounded sinus 

 of the ventral valve are also more characteristic of the latter species. 



I am very much inclined to identify this Nevada shell with Whitfieldia 

 tumida, as M. nasuta is scarcely more than a variety of it that obtains, in 

 its later stages of growth, a greater prolongation of the valves. If either 

 the Nevada or New York shells were found in association with M. tumida, 

 they would scarcely be distinguished in external characters as more than a 

 variety. For the purpose of more clearly presenting the relations of the 

 Devonian faunas of the Rocky Mountains and the eastern half of North 

 America, and while awaiting more material for study, we have retained 

 species under separate names that are considered as varieties of some well- 

 known species. 



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

 northwest of Eureka, Nevada. 



