HOPLOPAEIA AND PSEUDASTACUS. 343 



are known by the generic names of Hoploparia and 

 Enoploclytia, are abundant. 



The differences between these two genera, and between 

 both and Eryma, are altogether insignificant from a broad 

 morphological point of view. They appear to me to be 

 of less importance than those which obtain between the 

 different existing genera of crayfishes. 



Hoploparia is found in the London clay. It therefore 

 extends beyond the bounds of the Mesozoic epoch into 

 the older Tertiary. But when this genus is compared 

 with the existing Homarus and Nephrops, it is found 

 partly to resemble the one and partly the other. Thus, 

 on one line, the actual series of forms which have 

 succeeded one another from the Liassic epoch to the 

 present day, is such as must have existed if the common 

 lobster and the Norway lobster are the descendants of 

 Erymoid crustaceans which inhabited the seas of the 

 Liassic epoch. 



Side by side with Eryma, in the lithographic slates, 

 there is a genus, Pseudastacus (fig. 80, A), which, as its 

 name implies, has an extraordinarily close resemblance to 

 the crayfishes of the present day. Indeed there is no point 

 of any importance in which (in the absence of any know- 

 ledge of the abdominal appendages in the males) it differs 

 from them. On the other hand, in some features, as in the 

 structure of the carapace, it differs from Eryma, much 

 as the existing crayfishes differ from Nephrops. Thus, in 

 the latter part of the Jurassic epoch, the Astacine tjpe 



