268 bulletin: museum of comparative zoology. 



genera, including organisms of all kinds except the Bryozoa, about 

 half are not found in America. Of the genera common to the two 

 countries, a few make their first appearance in America in the Beekman- 

 town, a much larger proportion first appear in the Chazy or Stones 

 River, and a few do not appear in America till Middle or late Trenton 

 or even later. It is pointed out, however, that even in the case of 

 certain of the genera reputed to be in both countries, the Russian 

 representatives differ in marked ways from American species, and 

 closer research is bound to show greater differences instead of greater 

 likeness between the faunas of the two countries. 



The fauna of the American Beekmantown is very imperfectly known, 

 but the classes of fossils so far as relative abundance is concerned, are 

 ranked in the order of: — first, cephalopods; second, gastropods; third, 

 trilobites; fourth, ostracods; and finally brachiopods, cystids, and 

 bryozoans, all in small numbers. On the other hand, the Walchow 

 and Kunda formations have great numbers of trilobites and brachio- 

 pods, many cystids, cephalopods, and bryozoans, very few gastropods, 

 a few ostracods, and crinoids. The two groups agree in the absence 

 of pelecypods and corals. 



If there were no other evidence than that afforded by the time of 

 the first appearance of certain genera in Russia and America, it might 

 well happen that the Walchow and Kunda formations might be corre- 

 lated with the Chazy, but I do not see that they could be correlated 

 with any younger strata. The comparison of the Russian with the 

 Scandinavian sections, however, places such a correlation out of the 

 question, and Avhen one compares the faunas of these zones with the 

 fauna of the Ceratopyge formation of Scandinavia, he realizes the 

 antiquity of many of the groups, especially of the trilobites. Mega- 

 laspis, which is almost entirely confined to the Walchow and Kunda 

 in Russia, is well represented in the Ceratopyge limestone of Scan- 

 dinavia, one species being apparently common to the two formations 

 and regions. Symphysurus, Nileus, Xiobe, Eoharpes, and Ampyx 

 are other genera connecting these formations with the Ceratopyge 

 limestone, and even species of Nileus and Xiobe are said to be com- 

 mon to the two. 



On a priori grounds, we would not expect the Walchow and Kunda 

 faunas to have much in common with the Beekmantown, if they 

 are of the same age. The American fauna is an autochthonous one 

 developed in the interior continental sea, out of the late Cambrian 

 fauna. The fauna in Esthonia was, on the other hand, an invading 

 fauna which was derived primarily from the Ceratopyge fauna of 



