FOSSILS OF THE DEVONIAN. 145 



ties we place S. (M.) fimbriata Conrad, S. (M.) subundifera M. & W., (M.) 

 compacta Meek, and the Nevada shell under consideration. 



S. (M.) undifera and curvatus, var. undulata, Roemer, of the Middle De- 

 vonian of England and the continent of Europe, S. (M.) erubescens Eichwald 

 (Leth. Ross., p. 703, taf. 34, fig. 18), S. {M.} undifera, var. Takwanensis, 

 Kayser, from the Devonian of China, and S. (M.) undifera Ethridge, from 

 Queensland, all appear to belong to the same specific group and show 

 its wide geographic distribution. 



It may be more convenient to use the older name S. (M.} fimbriata 

 Conrad for the variety with the strong interrupted striae, as it occurs in the 

 Lower Devonian of New York and the Upper Mississippi Valley region, 

 and Roemer's name S. (M.) undifera for the smoother, world-wide distrib- 

 uted variety so well illustrated by Davidson. If so, all the species men- 

 tioned will fall under S. (M.*) undifera with the exception of 8. (M.)Jimbriata. 



Professor Hall (Pal. N. Y., vol. iv, p. 216) calls attention to 8. (M,) 

 setigera and S. (M.) pseudolineata as representing in the Carboniferous lime- 

 stone the type of S. (M.) finibriata, and Mr. Davidson (Mon. Brit. Dev. 

 Brach., p. 08) states that the resemblances between S. (M.) undifera and the 

 Carboniferous S. (Jf.) ovalis and S. (Jf.) pinguis are often so striking as 

 almost to lead one to believe that they are all mere modifications in shape 

 of a single species. 



We have called attention in describing S. (M.) glaber, var. Nevadensis, to 

 Prof. H. S. Williams' life history of S. (M.) l&visgldber, where he traces its 

 descent from certain Upper Silurian forms through S. (M.) fimbriata, S. (M.) 

 Icevis, S. (M.) prcematura, and considers S. (M.) pseudolineata as carrying on 

 the type into the Carboniferous. This arrangement we have accepted, but 

 the presence of the type of S. (M.) pseudolineata in the Lower Devonian 

 suggests the view that the two types S. {M.) undifera and S. glaber were 

 already differentiated in early Devonian times, and that the line of descent 

 of S. (M.) glaber and S (M.) pinguis and the group of species that each 

 represent were determined in the Upper Silurian age. As we have no rep- 

 resentations of the latter fauna in the West, further comparisons are omit- 

 ted, the reader being referred to Professor Williams' excellent paper for his 

 views of the Silurian representations of the type of Spirifera under consid- 

 eration (Ann. New Yoi;k Acad. Sci., vol. ii, 1881). 

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