2 5 8 



THE CRUSTACEA 



may be withdrawn. There is, however, great diversity in the de- 

 tails of structure of the " facial " region among the Brachyura, and 

 these are of considerable value as systematic characters. 



In the Scyllaridae among the Macrurous groups the cephalic 



FIG. 147. 



Head and anterior part of body from below. A, Xephrops iwrvegicus. B, Macrocheira 

 Kaempferi. C, Carpilius convextis. (Drawn by Miss G. M. Woodward.) ', antennnle ; a", 

 antenna ; a.m, ridge forming anterior margin of the mouth-frame and dividing the epistomial 

 area into epistome proper and endostome ; c, point where the lateral wing of the carapace 

 touches, or, in B and C, fuses with, the epistome ; e, eye, in C retracted into, and partly 

 concealed by, the orbit ; end, endostome ; ep, epistome ; ex, exopodite ; l.m, lateral margin 

 of buccal frame ; l.p, lateral process of rostral plate, which in C comes in contact with the basal 

 segment (2+3) of the antenna ; md, mandible ; mp, median process of the front (in B and C) 

 uniting with anterior process of epistome ; mxp 3 , third maxilliped ; r, rostrum or (in C) 

 frontal plate ; s.o, suborbital lobe forming floor of orbit ; t, in A, tubercle bearing opening of 

 antennal gland, in B and C, operculum covering the opening and probably representing the 

 reduced first segment of the antenna ; 1-5, the segments of the antennal peduncle. 



region is modified in a way that at first sight suggests the Brachy- 

 urous type, the eyes being widely separated and lodged in complete 

 orbits. In this case, however, the front unites in the middle line 

 not with the epistome but with the greatly enlarged antennular 

 somite. 



In the Alpheidae (Caridea) the anterior margin of the carapace 



