REVIEW OF THE PERMIAN FOSSILS. 
217 
T. concentrica, Spirifer hystericus, Chonetes sarcinulata and Productus C and ini, a re 
peculiar, in the west, to the carboniferous or subjacent formations. The com- 
parison of these twelve species of Brachiopods with those of Western Europe, 
appears, at first sight, to be indecisive of the question, as to the stage in the 
geological series in which we ought to place the Permian deposits of Russia. But 
without even quitting this class of Brachiopods, the consideration of their other 
species shows an amount of parallelism, in the modifications they have undergone 
simultaneously in both countries, which in itself excludes all doubt. Ihe Pio- 
ductus horrescens, for example, however distinguishable from the P. horridus, is 
evidently the analogue of this shell so characteristic of the Zechstein , and the 
disappearance of all the large carboniferous Producti with longitudinal striae, and 
their replacement by small spinose species, as well as the striking diminution of 
every species of Orthis, both in Russia and in the West of Europe, are strong- 
negative characters, which clearly establish the contemporaneity of distant strata, 
accumulated under the influence of analogous organic laws. 
The Dimyaria present eleven Permian forms in Russia, of which eight species are 
peculiar to the country, and three others to the rest of Europe. Among the shells of 
this class the Modiola is the most abundant genus in Russia, — a fact which is in 
perfect harmony with the distinguishing features of the system in other countries. 
The Monomyaria are less numerous, and are represented in Russia by seven 
species, four of which are peculiar to the empire, and three are already known in 
the Magnesian Limestone of the West. These three species all belong to the genus 
Avicula, which in Russia, as in all the other regions of the same geological age, offers 
several small smooth species, and is, above all, rich in specimens. Among the 
species peculiar to Russia, we may cite the Avicula Kazanensis, which there replaces 
the Avicula speluncaria of Germany, the existence of which m Russia is problematical. 
The Gastropods do not present any interesting result, except that of the very 
limited number of their species, which is in conformity with the general law we 
have remarked in the relations of the Permian fauna. So is it with the Cephalopods 
and Trilobites ; for the entire absence of the latter and the extreme rarity of the 
former, are completely in harmony with the facts observed m the other Permian 
regions of Europe. 
The small number of fishes enumerated up to the present day in Russia might at 
first seem to be less accordant with what has been observed elsewhere ; but we 
must remark, that it is rather to the want of sufficient researches, and also to the 
