98 GEOLOGICAL MEMOIRS. 



are the Graptolites and the Tentaculites. The former, which seem 

 most nearly allied to Virgularia or Sertularia"^, have been known 

 ever since the time of Linna^.us, and the number of species has been 

 increased to thirteen, although, as it seems to us, without due con- 

 sideration in some cases. 



These species are distributed throughout the rocks of the Silurian 

 system, though chiefly in the lower members. Whatever may be 

 the ultimate decision with regard to the actual zoological relations 

 of these animals, their geological place at least is well-determined, 

 since they rarely pass out of the Silurian series of rocks, and in 

 Russia as in Sweden they characterize its lower beds. In Esthonia 

 the schists which contain them are superposed directly on the Oholus 

 clay, and may be regarded as the equivalents of the aluminous schists 

 of Sweden. 



Graptolites are presented under two well-marked forms, those ser- 

 rated on only one side^ and those on which the two sides are thus 

 marked. Both of these appear to exist in Russia, since although 

 we have only met with G. Sagittarius, which we consider the repre- 

 sentative of G.ludensis, M. Eichwald has described a species under 

 the name of G. distichus which belongs to the latter group. These 

 bodies, tolerably plentiful in Bohemia, in the island of Sardinia, in the 

 Pyrenees t, in Brittany and Normandy, and in England, extend also 

 to the opposite coast of the Atlantic, where Messrs. J. Hall and 

 Emmons have described two species. 



Having as wide an extension as the Graptolites among Silurian 

 rocks, the Tentaculites are however not limited to that group, one 

 or two of the ten (?) species which have been mentioned by various 

 authors extending into the Devonian rocks of the Eifel. We have 

 also a Russian species in the Silurian limestones of Podolia, and an* 

 other in the Devonian beds of Voroneje; but these fossils do not de- 

 scend into the lowest beds of the Silurian system. They are widely 

 spread over the earth's surface, and are met with in the Silurian 

 rocks of the United States. 



Corals. — Of these animal remains J two species are particularly 

 abundant, the Chcetetes Petropolitanus in the lower part of the Si- 

 lurian system, and C, radians in the carboniferous rocks. Of these 

 the first occurs in Sweden and in England, in the same position, and 

 the second is found in England, in the carboniferous limestone near 

 Bristol, but is there much less common than in Russia, where it 



* Recently discovered near S. Beal by M. Boubee (Bui. de la Soc. Geol. de 

 France, 2iid Ser., vol. ii.). 



t .Tudgiug from some specimens of Graptolites wbich appear to possess roots, 

 and into the composition of which carbon enters, Mr. Vanuxem considers these 

 bodies as belonging to the vegetable kingdom. We have also ourselves been 

 frequently struck by the carbonaceous appearance presented by certain indivi- 

 duals. 



X The Russian Corals have been described by Mr. Lonsdale, who had only be- 

 fore him the imperfect specimens obtained by the authors, and who unfortunately 

 had not been able to avail himself of the fine collections at St. Petersburg. The 

 present notice is confined to some general facts which struck the authors during 

 the coiu'se of their travels. 



Ji 



