i So 



ANNULOSA. 



The best-known living Anomura are the Hermit-crabs or Sol- 

 dier-crabs (Paguridof), the Crab-lobsters (Porcellatuz), 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 Red 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 carapace 

 is usually very large, and the extremity of the abdomen is not 

 provided with any appendages. Most of the Crabs are littoral 

 in their habits, and have legs formed for walking. Others are 

 adapted for swimming, and the Land-crabs habitually live 

 inland. 



As before remarked, the Brachyurous Decapods are much 

 later in their appearance than the Macrura. The oldest 



known Crab, at present, is 

 the Pal&inachus longipes, de- 

 scribed by Mr Henry Wood- 

 ward from the Forest Marble 

 (Lower Oolites). In the 

 Cretaceous series Crabs are 

 tolerably abundant, one Cre- 

 taceous form belonging to 

 the recent genus Cancer. In 

 the Tertiary Rocks, and es- 

 pecially in the London Clay 

 (Eocene), remains of Crabs 

 occur in profusion. The 

 chief Tertiary genera are 

 Xanthopsis, Xantholites, Cancer (fig. 123), Grapsus, and Ebalia. 



Fig. 123. Cancer \Carpilius) macrochelus, 

 Tertiary. 



