328 CRUSTACEA. DECAPODA 



anterior and a posterior portion by a groove, — the cervical 

 sutiwe (b). The shield is often produced in front into a 

 rostrum (a). The gills are connected with the thoracic 

 appendages and segments, and are placed in a chamber 

 formed by the downward prolongation of the cephalo- 

 thoracic shield. The appendages on the head are (1) an- 

 tennules, (2) antennae, (3) mandibles, (4, 5) maxillae ; the 

 last three pairs serve as jaws. On the thorax the first 

 three pairs of limbs are modified as maxillipedes ; the 

 posterior five pairs (k — 6) are the ambulatory limbs, 



P 



Fig. 143. Glyphea regleijana, Oxfordian. a — c, cephalothorax ; a — 6, 

 head; b — c, thorax ; a, rostrum; c — e, abdomen; d, sixth abdominal 

 segment ; e, telson ; /, appendage of sixth abdominal segment ; 

 g, eye ; h—o, appendages of cephalothorax ; k — o, ambulatory limbs. 



X -j. 



which, in most cases, are uniramous ; they consist of seven 

 joints, and, as a rule, some of them terminate in pincers 

 or chelce. The name ' Decapoda ' is taken from these five 

 pairs of ambulatory limbs. The abdomen bears six, or 

 fewer, pairs of small appendages. The eyes are compound 

 and stalked. 



The Decapoda may be divided into three sections : — 

 (1) Macrura, (2) Brachyura, (3) Anomura. The last 

 section includes the hermit-crabs and hermit-lobsters and 

 is represented by only a few fossil forms. 



