FOSSILS OF THE DEVONIAN. 



141 



Spirifera (M.) Maia Billings. 

 Plate iii, figs. 1, la-e; pi. xiv, figs. 13, 13o. 



Athyris Maia Billings, 1860. Can. Jour., vol. v, p. 276, figs. 33, 34. 



Spirifera Maia Hall, 1867. Pal. New York, vol. iv., p. 416 5 pi. Ixiii, figs. 6-13. 



Athyris (?) Maia Nicholson, 1874. Pal. Prov. Ontario, p. 88. 



Compare Spirifera subumbona Hall. 1867. Pal.N.Y.,vol.iv,p.234,pl.xxxiii,figs.22-30. 



8. (M.)meristoides Meek, 1868. Trans. Chicago Acad. Sci., vol. i, p. 106, 



and 8. (M.) sublineatus Meek, ibid. p. 103. 



Professor Nicholson considers Spirifera (M.) Maia, as identified by 

 Professor Hall as, probably, a distinct species from Athyris Maia Billings, 

 and refers the Canadian species to the genus Athyris, with a query. 



The specimens used by Professor Hall in his determination, three of 

 which are illustrated on plate Ixiii of vol. iv, Paleontology of New York, are 

 now in the Hall collection in the American Museum of Natural History, 

 New York City, and are from Saint Mary's, Canada West, the typical lo- 

 cality of the species. They exhibit the narrow cardinal area and small tri- 

 angular fissure mentioned by Professor Hall, and also the variation in form 

 from elongate to broad ovate. Mr. Billings and Professor Nicholson failed 

 to observe the cardinal area and fissure which is frequently almost entirely 

 concealed by the incurved beak. 



The Nevada form corresponds with that from Canada West. Slight 

 differences, liable to exist in specimens of the same species from widely 

 separated localities, are not perceptible in the examples separated by an 

 interval of nearly 1,800 miles, and there are no perceptible variations in 

 form between the specimens occurring in the Lower Devonian horizon and 

 those of the limestone beds over 3,000 feet above. 



When comparing the adult shells with other species it is noticeable 

 that the more transverse forms approach the type of Spirifera (M.) lineata, 

 also the smooth variety of Spirifera (M.) undifera. If it were not for the 

 large series of specimens it would not be difficult to select three allied species, 

 but, with the intermediate forms, there is but one variable species which is 

 closely allied to Spirifera (M.) lineata and Spirifera ( M .) planoconvexus of the 

 Carboniferous. 



There is considerable variation of form among the large number of 



