110 GEOLOGICAL MEMOIRS. 



tion of organic beings, those of highest organization and most per- 

 fect structure in the class of Mollusca have been present, and that 

 throughout the long duration of geological periods there have been 

 many modifications of specific form, but no advance on the whole. 

 The testaceous Cephalopods were even much more abundant and 

 more varied in ancient times than they are now, and most of the 

 typical forms of that period are now lost. 



The Orthoceratite, which preceded the Nautilus and Goniatite, 

 may be looked upon as one of the earliest forms assumed for the 

 shell of these animals, since we find indications of this genus asso- 

 ciated even with the first traces of life, and if the species appear 

 less varied in form in the lower beds of the Silurian system than in 

 the upper deposits, this difference is compensated by the greater 

 profusion of individuals. Thus in Russia and Scandinavia the spe- 

 cies O. duplex and O. vaginatus fill entire beds by their remains, 

 while it is curious enough to observe that the genus becomes rare 

 in the Devonian rocks of Russia, differing therefore in that respect 

 from the rest of Europe. In fact, except O. vermicular is, remark- 

 able for the bead-like form of the siphuncle, the Devonian rocks 

 only present one species, of which we found some fragments at 

 Voroneje and to the north of Bielef. The whole number of Russian 

 species, according to our determination, is only eleven, and if we 

 add those quoted by other authors, it amounts to twenty ; the distri- 

 bution of the eleven being, five Silurian, one Devonian and five car- 

 boniferous ; but considering that on the whole more than 130 spe- 

 cies of this genus have been already described, it is probable that 

 many still remain to be discovered in Russia: and, in fact, besides 

 the five Silurian species described in our list, we have also frag- 

 ments (from the neighbourhood of Reval) less distinctly marked, and 

 belonging to two other species with transverse rings, one of which 

 resembles O. tuhicinella, Sow. None of the Russian species are 

 common to two formations in that country, but two of the Silurian 

 species described by us appear identical with Devonian species from 

 the Fichtelgebirge, although this apparent identity must be received 

 with some hesitation, because Orthoceratites afford so few good 

 specific characters, that distinct species may very possibly not be 

 determinable from the exterior. Of our five carboniferous species, 

 two, O. ovalis and O. calamus, are from the Ural, two, O. annU" 

 latus and O. ornatus, from the Valdai, and the other, O. Frearsiiy 

 from near Moscow. They are all rare and limited in their distri- 

 bution. The genera Blelia and Sannionites of Fischer are only 

 crushed or deformed Orthoceratites, and the Hi/olites of 'Eichwald 

 is nothing more than the interior of the siphuncle of O. vaginatus* 

 Like the Bellerophons, the Orthoceratites do not extend into rocks 

 of the Permian age. 



The genus Gomphoceras, proposed for those short Orthoceratites 

 of which the last chamber is swelled and the aperture narrow and 

 contracted, affords two species in Russia and one in Poland. Of the 

 two former, one is Silurian and the other Devonian, while the Po* 

 lish species appears to be identical with G* subpyriforme of the De* 



