IN MODERN SCIENCE. I3I 



elaboration of a few apparent exceptions and 

 doubtful cases. 



His second heading relates to the distribu- 

 tion in time of the genera and species of 

 brachiopods. This he illustrates with a series 

 of elabprate tables, accompanied by explana- 

 tion. He then proceeds to consider the animal 

 population of each formation, in so far as 

 brachiopods, cephalopods, and trilobites are 

 concerhed, with reference to the following 

 questions: (j) How many species are con- 

 tinued from the previous formation unchanged? 

 (2) How many may be regarded as modifica- 

 tions of previous species ? (3) How many are 

 migrants from other regions where they have 

 been known to exist previously ? (4) How 

 many are absolutely new species? These 

 questions are applied to each of fourteen suc- 

 cessive formations included in the Silurian of 

 Bohemia. The total number of species of 

 brachiopods in these formations is six hundred 

 and forty, giving an average of 45.71 to each, 

 and the results of accurate study of each 

 species in its characters, its varieties, its geo- 

 graphical and geological range, are expressed 

 in the following short statement, which should 

 somewhat astonish those gentiemen who are 



