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 Hme- 

 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,^ Xiobe, Pseuda- 

 saphus, Ptychopyge, Cyrtometopus, Cybele, Pliomera, and Plato- 

 polichas, do not occur in America. Of the remaining nine genera, 

 Xileus 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. 



1 The 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. 



