HOPLOPARIA 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 Hryma, 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 Hryma, much 
as the existing crayfishes differ from Nephrops. Thus, in 
the latter part of the Jurassic epoch, the Astacine type 
