120 M. Barrande on the Silurian System of Bohetnia. 



England or Sweden ; in the quartzites D, the analogy is 

 notably increased, and many forms are identical ; whilst in 

 the superior division these identities are very numerous and 

 extend over all the classes. It thus appears that in the 

 period of time represented by the Silurian formations of Bo- 

 hemia, certain modifications on the surface of the globe have 

 successively increased the facility of communication between 

 these three countries. In his special comparison of the Bo- 

 hemian fauna with that of other countries, the author gives 

 the chief place to England and Sweden, both from their 

 greater analogy, and because these countries are now ren- 

 dered classical in geology by the works of Sir R. Murchison 

 and other scientific observers. 



The author (p. 88-92) gives a table of the species common 

 to these three countries, but we can only note some of the 

 general results. First, the Crustaceans are few in numbers, 

 perhaps a result of their feeble means of transport,, and the 

 conditions which seems to tie down the species to narrow 

 limits. On the other hand the Cephalopods, great swimmers, 

 should be widely spread. This is seen in Bohemia, but the 

 bad preservation of the English and Swedish specimens does 

 not admit of exact comparison. The forms of Phragmoceras, 

 however, in all the regions confined to a short period, impress 

 a very decided character on the epoch. Again, the great 

 superiority in the number of identical species among the 

 Brachiopods depends chiefly on the easy difi^usion of such 

 light shells, by means of currents, and partly on the greater 

 attention given to this class of late. The Polyparia seem 

 also to present many common species, though the list is not 

 yet complete. Their great vertical extent, however, renders 

 this fact of less importance. 



On considering the table attentively, it appears that by 

 far the larger portion of the common species occur in Bohe- 

 mia in the lower limestone stage E, in England in the 

 Wenlock beds, and in Sweden in the Gothland formations. 

 These, therefore, are contemporaneous deposits, though as 

 some of the Bohemian forms ascend into the Lower Ludlow, 

 this limit must not be taken too strictly. On the other 

 hand the upper three stages, F, G, H, have few species in 



