134 THE LIFE OF CRUSTACEA 



animals. The existing species (Fig. 46) are all blind, 

 with only vestiges of eye-stalks, and they may be 

 readily distinguished by the fact that the first four, and 

 sometimes all five, pairs of legs end in chelae, no other 

 Decapods having more than three pairs of chelate 

 legs. The fossils occur in rocks of the Secondary 

 Period, from the Trias to the early Cretaceous. 

 Some of them, at least, had well-developed eyes, and 

 probably lived in shallow water. This was almost 

 certainly the habitat of those (Fig. 47) that are found 

 preserved in a marvellously perfect state in the litho- 

 graphic limestone of Solenhofen (famous for the 

 discovery of Arch&opteryx and many other remark- 

 able fossils), which is believed to have been deposited 

 in a lagoon. After the early part of the Cretaceous 

 epoch, the Eryonidea are no longer found as fossils, 

 and it is, at all events, a probable conjecture that 

 about that period they forsook the shallow waters 

 for the deeper recesses of the ocean, where their 

 descendants have held their own till the present day. 

 Another group of deep-sea Crustacea which has 

 affinities with certain fossil forms is the little family 

 Homolodromiidae among the Crabs. It has already 

 been mentioned that the Dromiacea are the most 

 primitive tribe of the Brachyura, and Professor 

 Bouvier has shown that among these the Homolo- 

 dromiidae approach most nearly to the lobster-like 

 forms from which the Crabs have been derived. He 

 has further shown that the members of this family 



