522 



s. iSHii : 



specimens." 15 In the specimens before me, the greater parts of the 

 mesosome does not exhibit contortion to any marked degree, though 

 in the hindmost parts a slight twisting, corresponding to that of the 

 metasome, may often be noticed. 



Thoracic legs. There are seven pairs of thoracic legs, arranged 

 along sides of the body on the dorsal aspect. They are all prehensile 

 in function and similar in structure. Legs of the first pair are the 

 smallest, those of the second not so large as any other of the more 

 posterior pairs. Each leg is composed of apparently five joints, 10 not 

 including the coxal piece ; of the joints the two proximal ones are 

 the longest, the third and fourth of a medium size, and the fifth the 

 smallest. The fourth is of a somewhat ovoid outline ; a set of two power- 

 ful muscles is seen arising from one end and converging towards the 

 base of the fifth joint, which is of a beak-like appearance and togethar 

 with the fourth forms a chelate arrangement. The cuticula of the 

 fourth joint is, in the parts which come in contact with the beak-like 

 fifth joint in the depressed state, is considerably thickened, and more- 

 over presents a more or less roughened surface. The distal end of the 

 third joint is provided with a number of minute obtusely pointed 

 cuticular processes (Pl. VII Fig. 5, c.p.). The third and fourth joints 

 seem to be firmly jointed together. No conspicuous muscle seems to 

 occur in the third joint. Measurements of the right leg of the sixth 

 pair from specimen C, as follows : 



1) G. O. Sars, — "An account of the Crustacea of Norway," vol. 2, Isopoda, p. 210, 



1899. 



2) According to the figures given by G. O. Sars (loc. cit.), it seems that the legs in 

 Athelges paguri (Rathke) are six-jointed. Sars also represents six-jointed legs for other 

 Epicaridan parasites. The third and fourth joints as represented in the figures of Sars 

 together seem to correspond to the single third joint of my specimens. There exists a 

 constriction near the middle of this joint ; it is less marked in the male than in the female 

 (Pl. VII Fig. 5). It probably indicates the origin of the joint by fusion of two originally 

 separate segments. The third joint is possibly a combination of carpus and meros, while 

 the first joint corresponds to the basos of an ordinary Isopod leg. 



