BARRANDE ON THE TRILOBITES OF BOHEMIA. Jo 



The family ol' crustaceans, which exclusively composes the fauna 

 of the next lower group (C), is not completely absent in (D). The 

 other families are here also represented, but the number both of 

 species and individuals is small. 



Of other fossils are found — 



1. Among Heteropoda, two species o^ Bellerophon, one of which 

 is B, acutusy Murch., and the other resembles B. hilobatus of the 

 same author. 



2. The Cephalopods only furnish us with some fragments of Ortho- 

 ceras, without either shell or siphuncle, and therefore not very easy 

 to determine. 



3. The Pteropods are represented by four species of Conularia, 



4. Among the Brachiopods are four species of Orthis, one of 

 which is O. semicircularis, Murch., and two appear to be new. 

 There is also a species of Orhicula. 



5. The Monomyaria and Dimyaria are represented by two species 

 of Avicula, of which the shells are absent, together wdth some casts 

 very indistinct. 



6. There is a species of Encrinite resembling the genus Agela- 

 crinites of Vanuxem. 



7. There are several corals, badly preserved, among which the 

 author recognises Porites pi/7'iformis, Lonsd. 



From this general sketch of the other fossils, it will be seen that 

 these beds exhibit great poverty, except in trilobites. This no 

 doubt is partly owang to the absence of calcareous deposit ; and it 

 appears that the trilobites could live in the Silurian seas, in water 

 charged with siliceous matter, unfavourable for the development of 

 raollusca. 



Before comparing this group with other Silurian deposits, it is 

 worth while to remark the total difference presented between its 

 fossils and those of the lower group (C) of the same division. 

 Between the two there is not one species, and hardly a genus in 

 common. Notwithstanding this, if we only judged of the succession 

 of deposits by their local relations, the quartzites near Ginetz would 

 appear to repose directly on the fossiliferous schists, owing to the 

 absence of the intermediate beds. 



In spite of this discordance of the fossils, the author brings the 

 two groups into the same division, in consequence of the predomi- 

 nance of trilobites in both. 



The author then compares this group, as occurring in Bohemia, 

 with the corresponding Silurian rocks of other countries, and com- 

 mences with Great Britain. He considers that his group (D) cor- 

 responds to the whole of the Low^er Silurian group of Great Britain 

 with the exception of the Llandeilo flags, which he concluded were 

 the analogues of his group (C) before described. He even believes 

 that the mineral and lithological character of the beds in the two 

 countries might almost be sufficient to determine contemporaneity 

 in this case. The subdivisions of the Caradoc sandstone he recog- 

 nises in sections exhibited near Beraun. The five subdivisions 

 mentioned by Sir R. Murchison he forms into two groups, the upper 



