308 



THE CRUSTACEA 



dromiidae. One of the oldest, and at the same time one of the 

 most completely known, is Palaeinachus (Woodward) from the 

 Forest Marble (Lower Oolite), which has many generalised characters. 

 Later forms belonging to Prosopon (v. Meyer) and other genera give 

 evidence, according to Bouvier, of the divergence of a Homoline 

 and of a Dynomeno-Dromiine line of descent leading to such forms as 



FIG. 185. 

 Eryon propinquus (from the Jurassic rocks of Solenhofen), under-side. (After Oppel.) 



Homolopsis (Bell) and Dromiopsis (Reuss) from the Upper Cretaceous, 

 and to the existing Homolidae, Dynomenidae, and Dromiidae. The 

 remaining Brachyura have not yet yielded results of so much phylo- 

 genetic interest. The Oxystomata appear about the middle of the 

 Cretaceous system and the Brachygnatha about the same time. In 

 the Tertiary many Brachyura are found, representing the chief 

 existing types of the group. 



