516 



CRUSTACEA MALACOSTRACA. 



Anteriorly it becomes more prominent, and abuts against the 

 base of the 2nd antenna, partially or completely limiting its 

 movement. In most Brachyura the orbit is extended as a 

 hollow in the side of the carapace, and the forward con- 

 tinuation of the pleural margin is to be sought in the floor of 

 the orbit, near the base of the eye stalk. In the Oxyrhyncha 

 the base of the 2nd antenna, epistome and side of carapace are 

 fused together, all trace of sutures being obliterated. 



,Ant 1 



,Ant* 



FIG. 316. Ventral surface of Carcinus moenas, male, showing the relation of the pterygo- 

 stomial region to the epistome in the Brachyura. The jaws and maxillipeds of the right 

 side of the crab have been removed. Abd abdomen ; aiiti first antenna ; ant- second 

 antenna ; Ch chelipeds ; Ep epistome ; Gr.g flap covering the opening of the green gland 

 on the second antenna ; Mn mandible ; mxp. 3 third maxilliped ; Oc eye ; Pt.s ptery- 

 gostomial flap. 



Another characteristic feature of the Brachyura is that the 

 rostrum is very short and united below with the front of the 

 epistome, by a median ridge passing between the bases of the 

 first antennae (Fig. 316). 



Orbits. In the Macrura the eye-stalks are inserted near 

 together in front of the first antennae and the eyes project 

 sideways. The edges of the carapace (pleura) are, as noted 

 above, excavated to give them play. 



In the Brachyura, in accordance with the transverse extension 

 of the front of the carapace, the eyes are generally set far from 



