2 68 



THE LIFE OF CRUSTACEA 



especially in the lithographic stone (Upper Jurassic) 

 of Solenhofen, and by somewhat doubtful specimens 

 from the earlier Trias. All these agree in having 

 the first three pairs of legs with pincer-claws, and 

 not differing greatly in size. Some of the Jurassic 

 and later fossils are of so modern a type that they 

 have been referred to the existing genus Penceus. 



The Upper Jurassic rocks also preserve the earliest 

 undoubted specimens of true Prawns of the tribe 

 Caridea, and some of these show swimming branches 

 (exopodites) on the thoracic legs, so that they were 

 probably related to the primitive family Acanthe- 

 phyridae, of which the existing members are found in 

 the deep sea. It is possible, however, that Caridea 

 were already in existence far earlier, for some of 

 the obscure Carboniferous forms seem to have the 

 broadened side-plates of the second abdominal somite, 

 which, so far as we know, are exclusively characteristic 

 of that tribe. 



The Reptantia, forming the other large division of 

 the Decapoda, also had their origin at least as early 

 as the Triassic epoch, where representatives of the 

 tribes Eryonidea and Scyllaridea are found. The 

 history of the Eryonidea has already been discussed 

 (p. 133) in dealing with the deep-sea Crustacea. The 

 oldest representatives of the Scyllaridea belong to a 

 family (Glyphseidse) now wholly extinct, and are in 

 many respects more primitive and lobster-like than 

 any of the living Spiny Lobsters and their allies 



