G2 



PROCEEDINGS OP WASHINGTON MEETING. 



almost simultaneously ; and, vice versa, a certain phase of development indicates a 

 certain geologic epoch, as if it were a single fauna developing in some particular 

 direction and presenting some local deviation of small importance, such as the 

 predominance of this or that species and the comparative rarity of another. 



Figure 21— The Development of the belemnitic Fauna at the End of the Jurassic and the 



Beginning of the Cretaceous. 



I now proceed to characterize these hranches, whose relations are indicated in 

 the accompanying diagram. The first comprises the greatly elongated forms, such, 

 for example, as have been described by Phillips under the name of Belenmites obelis- 



