CRUSTACEA OF THE PAST 267 



recognized in rocks of Cretaceous age from Lebanon. 

 This is a striking example of the way in which, by a 

 fortunate accident as it were, organisms apparently 

 ill-adapted for fossilization may occasionally be pre- 

 served. 



Of the Decapoda the geological history is tolerably 

 full, and it is possible to trace in its broad outlines 

 the course of evolution of the various suborders. 

 Here again it is likely that the beginnings of the 

 group are to be sought for in the Carboniferous 

 epoch, and some of the obscure shrimp-like forms 

 of that age show hints of an affinity with the 

 Decapods. In the Triassic epoch, however, and 

 more abundantly in the succeeding Jurassic, a 

 number of types are found which seem to include 

 primitive representatives of several of the existing 

 groups of Natantia and Reptantia. It is noteworthy 

 that among them are some forms (Mger, etc.) 

 resembling the existing Stenopidea, a tribe which 

 in some respects is intermediate between these two 

 suborders. In the Stenopidea the first three pairs 

 of legs bear pincer-claws, as in the Lobster, but the 

 third pair is much the largest ; and ^ger agrees with 

 them in this unusual character, though there is little 

 else, in what is known of its structure, to help to 

 determine its affinities. 



The tribe Penseidea, which occupies in many 

 respects a primitive place among the Natantia, is 

 abundantly represented in the Jurassic epoch, 



