THE EXTINCT GENUS ERYMA. 341 



decapod Podophthalmia to which the Astacomorpha belong 

 occurs in the Carboniferous formation. It is the gi nus 

 Anthrnp damon a small and very curious crustacean, 

 about which nothing more need be said at present, as it 

 does not appear to have special affinities with the Astaco- 

 morplw. In the later formations, up to the top of the 

 Trias, podophthalmatous Crustacea are very rare ; and, 

 unless the Triassic genus Pcmphix is an exception, no 

 Astacomorphs are known to occur in them. The speci- 

 mens of Pemphix which I have examined are not suffi- 

 ciently complete to enable me to express any opinion 

 about them. 



The case is altered when we reach the Middle Lias. In 

 fact this yields several forms of a genus, Eryma (fig. 80, B), 

 which also occurs in the overlying strata almost up to the 

 top of the Jurassic series, and presents so many variations 

 that nearly forty different species have been recognised. 

 Eryma is, in all respects, an Astacomorph, and so far as 

 can be seen, it differs from the existing genera only 

 in such respects as those in which they differ from 

 one another. Thus it is quite certain that Astacomor- 

 phous Crustacea have existed since a period so remote 

 as the older part of the Mesozoic period ; and any hesi- 

 tation in admitting this singular persistency of type on 

 the part of the crayfishes, is at once removed by the 

 consideration of the fact that, along with Eryma, in thf 

 Middle Lias, prawn-like Crustacea , generically iden- 

 tical with the existing Penceus, flourished in the sea 



