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 when 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, Niobe, Eoharpes, and Ampyx 
are other genera connecting these formations with the Ceratopyge 
limestone, and even species of Nileus and Niobe 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 
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