Rev. T. R. R. Stebbing on Amvphipodous Crustaceans. 339 



of H. LuhbocMana, This latter species lias the two pairs of 

 antennaj very nearly equal, although in the full-grown male 

 the lower antennte are noticeably longer than the upper. Here 

 the first gnathopods have only two or three hairs on the hinder 

 margins of the wrist and hand, whereas in H. Nilssoni these 

 margins are prettily fringed with hairs springing from bead- 

 like points of insertion, with the wrist-margin fuller and 

 more rounded. It must, however, be observed that in the 

 largest specimens of both sexes these limbs agree closely with 

 the figure given by Messrs. Bate and Westwood : the fringes 

 have almost disappeared ; the hand is widened near the palm ; 

 and a re-entering angle breaks the roundness of the hinder 

 margin of the wrist. The second gnathopods have the 

 following minute marks of difference : — In //. Xilssoni the 

 apex of the finger closes down into the extremity of the palm, 

 which is well defined by the angle (less and less obtuse with 

 advancing age) which it forms with the margin of the hand, 

 this margin bearing two or three hairs very near to the angle 

 just mentioned ; in the allied species the palm is defined by 

 two spines, and the hairs on the margin of the hand occupy a 

 small indentation about the centre of it, while the wrist is a 

 little more produced backwards. It is worthy of notice that 

 in the adults of both species the metacarpus of the second 

 gnathopods meets the hinder margin of the hand, thus occupy- 

 ing the space which in the young belongs to the hinder margin 

 of the wrist. In the case of H. Lubhocktana, if there could 

 be any doubt that these two forms of the second gnathopod 

 belong to the same species, it would be set at rest by a speci- 

 men in my collection, which obligingly exhibits both forms on 

 the same animal — the result, it may be presumed, of arrested 

 development in the smaller limb of the pair. 



In H. Lubbocktana the coxse of all the legs and the thighs 

 of the last three pairs are crenate, with minute hairs in the 

 angles ; in the other species, though the hairs are present, the 

 crenature is wanting or inconspicuous. 



The foregoing differences have been, we must admit, suffi- 

 ciently minute, and requiring tolerably careful observation 

 with a good light ; but a very transient glance at the pereio- 

 poda of the two species will suffice to remove all hesitation 

 as to their perfect specific distinctness. It will not be necessary 

 to do more than describe the last in each series, as all the five 

 pairs in each species have the same general character. In 

 H. Nilssoni, then, the metacarpus, wrist, and hand of the last 

 pereiopod are comparatively slender. The metacarpus is armed 

 behind with four spines, and two in front, its distal extremity 

 being conspicuously fringed with a set before and behind. The 



