BARRANDE ON THE SILURIAN CRUSTACEA, ETC. 9 



where pointed out, that the Class of Cephalopods is not repre- 

 sented in the First Fauna of Bohemia ; and this is the case 

 •wherever this fauna occurs, — in Sweden, Norway, England, and 

 the United States. It is in the Second Fauna that the Cepha- 

 lopods first appear ; and even in this we have, however, as yet 

 discovered only badly-preserved fragments of a rare species of Ortlio- 

 ceras (without referring to those species of OrtTioceras and Cyrto- 

 ceras occurring in the " colonies*" of the Stage 1), and belonging to 

 the Third Fauna, in which they again appear). In Russia, Scandi- 

 navia, and North America the Second Fauna is more richly stocked 

 with Cephalopods than in Bohemia ; and there exists a rather large 

 number of Orthocerata with wide excentric siphuncles, — a group 

 which is wanting in the Silurians of Bohemia, England, France, 

 Spain, and Portugal. The entire absence of limestones in my Stage D 

 may well explain the nearly total absence of Cephalopods in my 

 Second Fauna. For as soon as calcareous deposits come in at the 

 base of my Upper Division, the Molluscs also appear, and are soon 

 developed in such a richness of form, that in this respect no other 

 country can be compared with Bohemia. In my Stage E, eight 

 genera appear together, all respectively in their greatest development. 

 Three of these. Nautilus, Gomphoceras, and Ascoceras, are limited 

 to this Stage ; five, Lituites, Trochoceras, Orthoceras, Cyrtoceras, 

 and Phragmoceras, pass upwards into Stage F, where the two latest 

 genera, Gyroceras and Goniatiies, then come in ; all the older types, 

 as shown by the diminution of the number of their species, having 

 already lost their vital force. In fact the seven genera of Stage F, 

 taken altogether, scarcely afford ith so many species as the eight 

 genera in Stage E. This decrement goes on in Stage G, where there 

 are only three genera, Gyroce7'us, Orthoceras, and Cyrtoceras, with 

 but few species. Lastly, in Stage H, only the depauperated remains 

 of Orthoceras and Lituites present themselves. 



The ti'ansition between my calcareous Stages takes place in a 

 nearly imperceptible manner, and without the traces of any revolu- 

 tion, so that it is difficult to comprehend the sudden disappearance 

 of so many forms of Cephalopods from this ancient sea of Bohemia ; 

 and we are thus led to accept the existence of a natural law deter- 

 mining the duration of the different animal forms, independent of the 

 physical disturbances which continually at one place or another con- 

 vulse the whole surface of the earth. 



The succession of specific forms of Cephalopods is very evidently 

 seen in Bohemia, whether we regard them as a Avhole, or look at the 

 several genera. The Ce})halopods, therefore, could be employed, 

 equally as well as the Trilobites f, for distinguishing the different 

 Stages, each of which has its own particular characteristic species ; 

 there being only very few species that are continued through several 

 Stages. As my researches in this Class are not yet finished, I cannot 

 accurately lay down the number of species in the several Stages ; but 

 at another time I will return to this subject. 



[* See Quart. Journ Geol. Soc. vol. viii. Part ii. Miscell. p. 37. — Transl.] 

 [t See Quart. Jouni. Gcol. Soc. vol. viii. Part ii. Miscell. p. .'U,— Tr.vnsl ] 



