710 THE VOYAGE OF H.M.S. CHALLENGER. 



a narrow plate along the inner margin of the propodos, and is studded with short, stiff 

 hairs of ecpial length. 



The second pair of gnathopoda (fig. li) is larger than the first; the coxal joint is 

 broad ; the basisal joint is short and broad, and has the inner margin fringed with fine 

 hairs, while the outer supports a long, slender, compressed ecphysis, distally fringed with 

 small hairs ; the ischium is broad at the base, slightly curved, and narrows distally, form- 

 ing a long and tapering operculiform plate ; the next succeeding joint is short and broad, 

 and articulated with the preceding obliquely across its longitudinal plane, and the terminal 

 joint is sharp pointed, and both are thickly fringed with hairs on the inner margin. 



The first pair of pereiopoda is wanting in our unique specimen, and so are all the 

 others excepting the right one of the second pair. In this the carpos is triangulate ; the 

 propodos is about equal to the entire length of the animal, it is slightly curved in a 

 longitudinal direction, broader near the base than at the distal extremity, the cross-section 

 is ovate, being rather more distended on the outer than on the inner side ; the distal 

 extremity is produced to a pollex that has two cusps on the inner surface and is 

 slightly curved at the apex, where it corresponds with that of the dactylos ; the 

 dactylos is short, deep, arcuate on the outer margin and unicuspidate on the inner, 

 corresponding with the depression between the two cusps on the pollex. 



This chela is therefore, in proportion to the size of the animal, a very weighty 

 appendage, and, as in all Crustacea where the organ is so monstrously developed, it is 

 useless in its adaptation to supply the mouth, and, therefore, is probably of value as an 

 anchorage, by its great weight enabling the animal to hold its position more easily and 

 with less muscular effort. 



The pleopoda are short and biramose, the inner branch being furnished with a 

 stylamblys. The rhipidura is wanting. 



Observations. — The specimen does not appear to have been obtained by the Challenger 

 at any of the recorded stations, and it might easily be taken for that described by 

 Professor Milne-Edwards under the name of Pontonie eiiflee, 1 whose description I 

 translate as follows : — 



" No spine near the base of the external antennaa. Carapace having the lateral 

 margins very much inflexed ; rostrum reaching nearly to the extremity of the scapho- 

 cerite. Second pair of pereiopoda very large and nearly cylindrical. Length, one 

 inch." But, since the name applied by Milne-Edwards is suggestive of an inflated 

 or swollen appearance, I have hesitated to believe this to be the same species, the more 

 especially because the author says 2 that a short carapace is characteristic of the species 

 of this genus, and this coincides with the figure given by Dana, whereas in our species 

 the body is by no means inflated, although the chela is a large and weighty appendage ; 

 the pleon instead of being wide gradually narrows posteriorly from the first somite. 



1 Hist. Nat. Crust., torn. ii. p. 360. 2 Lot. «'(., p. 358. 



