CRUSTACEA OF THE PAST 269 



(Palinuridae and Scyllaridae). Forms with greatly 

 thickened antennae, indicating a transition to the 

 Pahnuridse, begin to appear in the Jurassic ; and 

 in the later Cretaceous a genus, Podocrates, occurs 

 which is hardly to be distinguished from Linuparus, 

 now living in Japanese seas. The Scyllaridae have 

 the antennae modified into broad shovel-like plates, 

 and perhaps take their origin from Cancrinus, in the 

 Solenhofen lithographic stone (Jurassic), which has 

 broad and apparently flattened antennae. True 

 Scyllaridae are certainly found in Cretaceous de- 

 posits, and some, from the Upper Chalk, are even 

 referred to the existing genus Scyllarus. 



The Anomura are almost unknown as fossils, but 

 the true Crabs, or Brachyura, are abundantly repre- 

 sented. They first appear about the middle of the 

 Jurassic epoch, and, as already pointed out, the 

 earliest forms (Prosoponidae) are referred to the 

 Dromiacea, and appear to be closely related to the 

 primitive Homolodromiidae now living in the deep sea 

 (p. 134). One of the oldest, and at the same time one 

 of the most completely known, is Protocarcimis, from 

 the Great Oolite of Wiltshire, which is preserved (in 

 the only known specimen) with the abdomen partly 

 extended, possibly indicating that the abdomen was 

 less closely doubled under the body than in modern 

 Crabs. 



The next group of Crabs to appear are the Oxysto- 

 mata, which are found from the middle of the 



