108 GEOLOGICAL MEMOIRS. 



The family of Ostracece, which has formed so important a part of 

 the submarine fauna ever since the commencement of the secondary- 

 period, was only previously represented in Russia by a very small 

 species discovered in the Permian limestones of Itschalki near Ar- 

 zamas. 



Gasteropoda. — From the first introduction of organic life upon 

 the earth down to the present time, the Gasteropods have followed 

 a law of constant progression, and the small proportionate number 

 of animals of this class in the ancient seas compared with the im- 

 portant place they occupy in the existing creation, is one of the 

 characteristic features of the palaeozoic fauna. Capulus or Pile- 

 opsis, and the genus which has been separated from this group 

 under the name Acroculia, represented in the palaeozoic formations 

 of Europe and America by twenty-five species, offers but two spe- 

 cies in Russia, one of which only is known to the authors. Such is 

 not the case with Euomphalus, a genus which, owing to its abun- 

 dance throughout the palaeozoic seas, may be considered as one of 

 the most important types among the Gasteropoda of that period. 

 We have found seven species in Russia, and including those men- 

 tioned by other authors, the whole number appears to amount to 

 sixteen, nearly one-third of the species at present known. Of 

 our seven species, one occurs in each of the two lower systems, 

 and the remaining five are carboniferous. £J, gualteriatus^ the Si- 

 lurian species, is known to be characteristic of the lower beds, and 

 is found not only in Sweden and Norway but also in the island of 

 Newfoundland and the United States of North America. The De- 

 vonian species, E. Voronejensis, is the only one peculiar to Russia ; 

 and of the carboniferous species, E. pentangulatus, E. catillus and 

 E. cequalis were distributed at that time throughout the greater part 

 of the European ocean. 



In singular contrast with this group, we find Pleurotomaria af- 

 fording in Russia a mixture of known forms with new species, and 

 developed to a smaller extent there than elsewhere in comparison 

 with the Gasteropoda in general. Thus, whilst the general palaeozoic 

 fauna contains sixty species, there are in Russia only nine, of which 

 number we have either described or seen seven. Most of the species 

 are carboniferous, and we may mention amongst them P. Yvanii, a 

 Belgian species, which we found on the eastern flanks of the Ural. 

 On the eastern flank of that mountain-chain, but further towards 

 the north and in the older beds, we find in tolerable abundance a 

 pretty species of Murchisonia, which M. von Buch has identified with 

 M. cingulata. Russian species of Trochus and Turbo have been men- 

 tioned by M. Eichwald as occurring in the Silurian rocks of Estho- 

 nia, but they are rare. This however is not the case with Melania 

 rugifera {Loxonema^ Phil., Chemnitzia, De Kon.), which we have 



posited in the Paris Museum, show how widely extended is this generalization 

 with regard to the development of Pecten during the carboniferous epoch. In 

 fact, we find the species of Productus and Spirifer, as well as the plants collected 

 by this naturalist near Hobart Town, all indicating deposits of the carboniferous 

 period, and amongst these fossils are associated some beautiful species of Pecten. 



