DECAPODA. 



393 



series, especially in the London Clay (Eocene), are numerous 

 remains of Macrura, some of which have been referred, with 

 more or less doubt, to 

 such living genera as 

 Astacus and Palinurus. 

 TRIBE II. ANOMURA. 

 The Anornurous De- 

 capods are distinguish- 

 ed by the condition of 

 the abdomen, which is 

 neither so well devel- 

 oped as in the Macrura, 

 nor so rudimentary as 

 in the Brachyura. The 

 abdomen does not take 

 any part in locomotion, 

 and does not terminate 

 posteriorly in a caudal 

 fin. The penultimate 

 segment of the abdomen, 

 however, is mostly fur- 

 nished With more Or leSS **& --Zryn arcttforrrus Middle Oolites. 



(Solenhofen Slates.) 



well - developed appen- 

 dages. The best -known living Anomura are the Hermit- 

 crabs or Soldier-crabs (Paguridce), the Crab-lobsters (Porcel- 

 lance), and the Sponge-crabs (Dromia). 



The Anomura are of small importance as fossils. They 

 commence in the Secondary period, a few forms having been 

 described from the Oolites, and a greater number from the 

 Cretaceous rocks. In the Tertiary period Anomurous Crus- 

 taceans are not uncommon ; and the genus Pagurus itself 

 appears to be represented in the Eed Crag (Pliocene). The 

 Dromilites of the London Clay is supposed to be related to 

 the living Dromia. 



TRIBE III. BRACHYURA. The " Short-tailed " Decapods or 

 Crabs are distinguished by having a rudimentary abdomen, 

 which is tucked up beneath the cephalothorax. The cara- 

 pace is usually very large, and the extremity of the abdomen 

 is not provided with any appendages. Most of the Crabs 



