J. F. JAMES — THE GENUS SCOLITHUS. 43 



Logan in 1S52. Since then some authors have considered it as possibly a fossil 

 plant, but the great majority recognize it as a worm burrow. Billings, in 1869, 

 was the only one to refer it to the sponges. 



There have been described of the genus from North America the following 

 species : 



Scolithus {Fucoides) shepardi, Hitchcock, 1833 (Triassic). 



S. linearis, Haldemann, 1840 (lower Cambrian). 



S. {Fucoides) verticalis, Hall, 1843 (Portage). 



S. clintonensis (n. sp.), proposed for 8. verticalis, Hall, 1852, preoccupied (Clinton 

 and Medina). 



8. canadensis, Billings, 1862 (Potsdam). 



S. minutus, "Wing, 1877 (Calciferous). 



S. tuberosus, Miller & Dyer, 1878 (Cincinnati). 



S. (Arenicolites) woodi, Whitfield, 1880 (Potsdam or St. Croix). 



S. delicatulus, U. P. James, 1881 (Cincinnati). 



8. dispar, U. P. James (= Eophyton dispar), 1881 (Cincinnati). 



S. minnesotensis (n. sp.,), Winched, 1884, described but not named (St. Petero). 



The geological range of the genus appears from this list to be from the lower 

 Gambrain to the Triassic. 8. shepardi from the Triassic does not differ in any 

 essential respect from S. linearis from the Cambrian. It is impossible to separate 

 S. verticalis of the Portage from 8. clintonensis of the Clinton and Medina, or either of 

 these from S. linearis. As we have already shown, S. canadensis and S. linearis may 

 be considered identical ; while S. minutus from the Calciferous and S. woodi from 

 the upper Cambrian of the Mississippi valley may be said to be separable by no de- 

 finable characters. S. delicatulus from the Cincinnati differs from S. mi nut us only in 

 having the cavities of the tubes filled instead of being hollow. Finally, S. minne- 

 sotensis from the St. Peter is the same, so far as characters go, as S. linearis from the 

 lower Cambrian. 



It cannot be considered as at all probable that the annelid living in the lower 

 Cambrian and making the perforations we know as S. linearis persisted in the same 

 form through all later geological periods into Triassic time. Mr. Walcott does not 

 think it probable that the same species ranged even through Cambrian time, to say 

 nothing of a much greater time-range. Yet he places forms from the lower and 

 from the upper Cambrian under the same specific name. On the same principle 

 we should unite all the species, in whatever geological horizon they may occur, 

 under one name, for there are no characters to distinguish one from another. But 

 this docs not seem advisable, and under the circumstances I would propose that the 

 geological position shall decide the name to be used. Thus, 8. linearis might be 

 applied to forms from the lower Cambrian rocks of the eastern United states; S. 

 canadensis to those occurring in upper Cambrian strata of the eastern United States, 

 and S. woodi to those from strata of similar age in the upper Mississippi valley; S. 

 mi nut a* might he t lie name f< »r t he 6 >rni in Calciferous strata ; S. minnesotensis might 

 be applied to the forms from the St. Peter, and 8. delicatulus to those in Cincinnati 

 rocks; S. clintonensis might be applied to those from Clinton and Medina strata, 5. 

 verticalis to those from the Portage, and S. shepardi to those from the Triassic. It is 

 probable, also, that a name should he given to forms collected from other horizons, 

 say S. arizonicus to the form from the Grand canon in Arizona. 



Several objections may be urged against such an arrangement. One of these is 

 that ii robs the genus of all value as indicating the age of the rocks in which it 



