DE VERNEUIL AND D ARCHIAC ON RUSSIAN PALAEOZOIC FOSSILS. 101 



niacrinites, Platycrinites and Rhodocrinites, quoted by M. Eichwald 

 as occurring either in Esthonia or the Valdai Hills. The identi- 

 fications of this author having unfortunately been made after an ex- 

 amination of fragments only of the stem, cannot be received with 

 confidence, especially when it appears that, contrary to what hap- 

 pens in other classes, there are so many species common to two or 

 more systems. We may however except from this remark the beau- 

 tiful head figured by the Duke of Leuchtenberg under the name of 

 Apiocrinites dipentas. 



Brachiopoda.-^Oi all the classes of animals which peopled the 

 palaeozoic seas, there is none more worthy of attention than the 

 Brachiopoda, and none is more generally distributed. In whatever 

 locality, at whatever part of the group of deposits, or whatever be 

 the nature of the rock which we examine, we very commonly find 

 that there is little beyond the remains of these animals to guide us 

 in our geological investigations. In a collection like that acquired 

 by ourselves during a rapid journey and under circumstances in 

 which the proportionate abundance of the various species of animal 

 remains is not disturbed by the undue preponderance of rare and 

 exceptional species almost always met with in local collections, the 

 Brachiopods form almost half the whole number, — a decided proof 

 of the important place which these animals occupied among the 

 population of the ancient seas. 



The causes which contribute to this great development of indivi- 

 duals in point of number having been also favourable to the esta- 

 blishment of new forms derived from the primitive type, a rich 

 variety of each form has resulted, constituting a number of genera 

 peculiar to this period. Observations are offered on these in the 

 body of the work, so that we confine our present remarks within 

 moderate limits. 



The total number of species of TerebratulcB in Russia amounts to 

 forty-four, according to our own actual observations, but must be 

 extended to fifty-two if we include species cited by other authors. 

 Considered only so far as regards the Russian empire, these species 

 are characteristic of the various formations in which we meet with 

 them, except T, reticularis^ which is both Silurian and Devonian, 

 T. elongata carboniferous and Permian, and T. concentrica^ ^ which 

 passes at once from the Devonian rocks, where it is constant, into 

 the rocks of the Permian age, without appearing at all in the car- 

 boniferous deposits between them. If however we take into account 

 the palaeozoic rocks of other parts of Europe, we find, besides the 

 instances above-quoted, two species common to the Silurian and 



* The true T. concentrica has been met with in four localities in Russia, but 

 one from the Ural (figured by the authors, pi. 8. fig. 10) is distinguished by 

 the small furrow which separates the hgauient of the ventral valve. In the De- 

 vonian limestones of the Asturias in Spain there exist five or six species charac- 

 terized by this same furrow, and one of them, absolutely identical with theUralian 

 species, has been named by the authors T. Pelapayanensis (Bui. dc la Soc. Gcol. de 

 Fr., 2nd Ser. vol. ii. p. 448. See also Quart. Gcol. Journ. vol. ii. Part 2. p. 65, 

 where this memoir is translated). 



