102 PROCEEDINGS OF WASHINGTON MEETING. 



of occasional direct intercourse between the southern palearctic and nearctic 

 faunas. To the geologists and paleontologists who try to trace the origin and 

 migrations of extinct faunas and their evidence as to the physiography of the past, 

 the question is also of primary importance. 



The evidence that would be most conclusive now, of course, lies buried beneath 

 the Atlantic, and the paleontologist has to turn to America to see whether he can 

 trace among its fossils the origin of any of the constituents of the old world faunas, 

 and, if so, to see if he can discover when they entered the European area and by 

 what route they traveled. 



Any comparison of the European and American faunas that might be made with 

 this end in view must be conducted with greater care than it would be possible for 

 any one paleontologist to give to the whole of the evidence. A mere examination 

 of lists of species is quite inadequate. Hence probably more reliable data can be 

 gained from the detailed study of one group than from an attempt to handle all 

 the available evidence; at least, this is all the present writer can attempt. The 

 echinoidea offer especial advantages: the bathymetrical range of the species is 

 fairly restricted ; the deep-sea forms are very easily distinguished ; the adults at 

 least, and in some cases the young, are practically non-migratory ; the echinoids 

 are mostly tropical or temperate in habitat; they occur in abundance from the 

 Carboniferous to the present; and, finally, as their classification rests upon the 

 hard parts, their affinities can be more definitely decided than in the cases of most 

 other classes. Hence in this paper attention is restricted to the echinoidea. It 

 must, however, be admitted that conclusions based on one class alone are likely to 

 be modified when the evidence of all the other groups is worked out. The final 

 conclusion will probably be the mean of the results given by the independent study 

 of the different divisions of the animal kingdom. 



The Carboniferous Faunas. 



Neglecting the problematical Silurian and the rare Devonian echinoidea as Lfiviin: 

 no adequate data for comparison, it is with th" Carboniferous system that the 

 species become sufficiently numerous to form definite faunas. 



In .Mr. S. A. Miller's useful "Catalogue of North American Paleozoic fos>ils" we 

 find a fairly long list of Carboniferous echinoidea. Deducting one or two syno- 

 nyms, the list stands as 41 species and I<> genera, to which must be added several 

 new species recently described and several undescribed forms that occur in the 

 American museums. Of this fauna of about 50 species, not one representative 

 occurs in Europe. It is true that 20 of these belong to the genus ArcJiseocidaris, and 

 most of them have been based on spines and isolated plates; and that while the 

 discovery of better material would probably reduce the number of species, it might 

 at the same time demonstrate the identity of some of them with European forms ; 

 but at present I feel bound to admit that I have seen no evidence of the existence 

 of any one Carboniferous echinoid on both sides of the Atlantic. The comparison 

 of the genera is still more valuable and brings out a great difference between the two 

 faunas. Of the ten American genera only three occur in Europe, viz, Archseoci- 

 daris, Palsechinus, and Perischodomus.* The other seven genera are peculiar to 



* Eocitlaris may seem an additional genus, but the European species referred to it really belong 

 to Cldaris. and the name has been abandoned as a synonym. The specimen described by Vanuxe'm 

 as Eocidaris drydenensis proves to belong to a very different genus. The type is now in the New 

 York State museum at Albany. 



