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264 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
River, and it has been by no means unusual, even among European 
text-book writers, to consider the upper formation (Orthoceras lime- 
stone) as of Black River age, this being primarily due to the abundance 
of large cephalopods and of trilobites in both the Orthoceras limestone 
and the Black River limestone. Bassler’s argument seems to be based 
largely upon the state of development rather than on identity of 
species of the bryozoan fauna, for of eleven species in the Glauconite 
limestone and fourteen in the Orthoceras limestone, only two in each 
are identified by him with American species. 
Lamansky has listed 142 species and varieties of fossils from these 
two formations, and Schmidt and Bassler have since added enough 
more to bring the number to about 186. Of these, seventy-seven are 
trilobites, forty-five brachiopods, nineteen cystids, twenty-six bryo- 
zoans, eleven cephalopods, four pteropods, and four gastropods. 
Trilobites. 
Eighteen genera of trilobites are listed, and of these, most of the 
prominent ones, namely, Asaphus, Onchometopus,! Niobe, Pseuda- 
saphus, Ptychopyge, Cyrtometopus, Cybele, Pliomera, and Plato- 
polichas, do not occur in America. Of the remaining nine genera, 
Nileus and Eoharpes are found in the typical Beekmantown, Megalas- 
pis may occur in the Beekmantown, provided the few American species 
which have been referred to that genus really belong,” and Illaenus is 
common in the Beekmantown, while the other genera, Ceraurus, 
Remopleurides, Lichas, Pterygometopus and Ampyx make their 
first appearance in American faunas in the Chazy or later formations. 
To these five genera belong eighteen species, mostly rare trilobites, 
and of the eighteen species, eight are confined to the upper of the two 
formations. 
These figures indicate very clearly the total unlikeness of the trilo- 
bite faunas of the Beekmantown of America and the Walchow and 
Kunda of Russia. Of eighteen genera only four are common to the 
two, nine are entirely unknown in America, and four make their 
first American appearance in the Chazy. In America, Lichas appears 
first in the Silurian. 
1The American species referred to this genus by the writer must probably be included 
with Brachyaspis. ‘ 
2 Megalaspis beckeri Slocum is almost certainly not a Megalaspis. 
