REPORT ON THE AMPHIPODA. 1329 



name " Onidium spinosum." It may be takcu for granted that they represent the 

 species Oniscus spinosus of Fabricius ; they give a dorsal, a ventral, and a lateral view 

 of the animal, and vary in length from four inches and three-quarters to nearly five 

 inches and a half. Since, with the other Amphipoda which he represents, Parkinson 

 gives life-size figures as well as the enlarged ones, it may be presumed from the absence 

 of any small figure of " Onidium spinosum," that five inches w T as approximately the 

 length of the actual specimen, or not so greatly in excess of it as to be thought to 

 demand a more exact specification of the real size. In general appearance and 

 details, and in particular in the antennae and uropods, the figures agree with the male 

 specimen brought home by the Challenger, but in the fifth peraeopods there is the 

 remarkable thickening of the fifth joint, which has been described for the female only 

 and to which Fabricius no doubt alludes when describing this joint as " articulo ultimo 

 clavato." 



The male and female specimens which I have here placed together under the name 

 Cystisoma spinosum (Fabr.), are regarded by Bovallius as representing two distinct 

 species, the male being named by him Thaumatops neptunus (Guerin-Meneville), and 

 the female Thaumatops pellucida (von Willemoes Suhm). In the female, the upper 

 antennae are longer than in the male, and have the termination of the long second 

 joint swollen, containing a gland ; the fifth joint of the fifth peraeopods is swollen, 

 smooth -edged, and full of gland-cells ; the outer ramus in each pair of uropods is 

 longer than the inner, and swollen near the apex, containing a gland. These make a 

 striking group of differences, outside of those which are obviously sexual, but it wdl be 

 noticed that there is probably a correlation between the differences, since all are 

 connected with glandular contents of the organs concerned, in the lengthened antennae 

 at one end of the animal, and the lengthened rami of the uropods at the other, whde in 

 the peraeopods, midway between these two extremities, it is easy to understand that 

 the dentate edge, useful to a laminar joint, would be of no service to the joint when 

 by the packing with gland-cells it becomes more or less cylindrical. In Parkinson's 

 figure of "Onidium spinosum" we find the antennae and uropods agreeing with the 

 Challenger male specimen, but the fifth peraeopods agreeing with the Challenger female 

 specimen. From the perplexity which thus arises, it would be easy to escape by 

 saying that Parkinson's is a third intermediate species between the other two, and 

 future discoveries may prove this to be the true solution, but for the present I 'am 

 disinclined to ground specific distinction on characters which may turn out to be merely 

 sexual. Moreover, the differences, though striking when discussed on paper, are com- 

 paratively trivial when contrasted with the still more striking resemblance, both in 

 general and in detad, which the two fine specimens present. 



(ZOOL. CHALL. EXP. — PAST LXVII. — 1888.) Xxx 167 



