14G THE VOYAGE OF H.M.S. CHALLENGER. 



the following pages, that in certain Sphseromids the males only are furnished with 

 uropoda, in which the exopodite is long and curved, the endopodite being fixed, and 



rudimentaiy, while in the females both endopodite and exopodite are subequal; the 

 genus CiMcsea is distinguished from Nessea, or at least is supposed In he distinguished, 

 by the long spine into which the median dorsal region of the anterior abdominal 

 segments is prolonged. This, however, has been shown by Mr. Haswell to be, at least 

 in one species, 1 a sexual character, the spine being entirely absent in the female; some 

 species of Cilicsea have uropoda like those of Cymodocea, while in others the exopodite 

 of the uropoda is alone fully developed. But a more striking argument, perhaps, as to 

 the impossibility of making the form of the uropoda a basis of generic distinction, i to 

 be derived from the study of a new deep-sea species described in the present Report 

 (p. 150); of this species, which I have named Cymodocea abyssofum, there are two 

 specimens, one a male and the other a female; they were obtained at the same Station, 

 and agree so exactly in every detail of their structure, except in the form of the uropoda, 

 that I cannot but regard them as belonging to the same species; in the male the uropoda 

 are like those of the typical Nesiea, while in the female the two rami are equally 

 developed, as in Cymodocea. M. Hesse 2 has also brought forward very strong arguments 

 in favour of regarding many supposed generic distinctions as being merely sexual 

 differences. 



Mr. E. J. Miers, in his account of the Crustacea dredged by the " Alert," has referred 

 to the probability that Nesxa latreillei is probably only the male of Cymodocea. 



I am able to confirm this supposition by the examination of a scries of this species in 

 the Challenger collection. The specimens were obtained at Station 190, and consist of 

 one fully developed male, several females, and one young male, in which the dorsal 

 spine is just beginning to make its appearance, though the uropoda have equal rami like 

 the female; in the fully developed male the fixed endopodite is rudimentary, while the 

 exopodite is a long, stout, curved joint. 



All the specimens were obtained at the same haul of the dredge, and are so alike in 

 other respects that 1 cannot but regard them as belonging to one and the same species 



The genera Isocladus of Miers, and Zuzara of Milne-Edwards, have been dis- 

 tinguished from Sphseroma by the presence of a long spiny out-growth of the last 

 segment of the thorax ; I have lately received, through the kindness of Mr. G. M. 

 Thomson, specimens of Isocladus armatus from New Zealand, in some of which this spine 

 was present and in others absent. Mr. Thomson expressed to me in a letter his 

 suspicions that this difference might in reality prove to be sexual, in which case there 

 would be no necessity to remove the species from the genus Sphseroma; a careful 

 examination of the specimens forwarded has convinced me that Mr. Thomson's suspicions 

 are correct, and that it is only the male which has a dorsal spine, the female being a 



1 Cilicsea hystrix, Proc. Linn. Soc. N.S.IF., vol. vi. p. 185. 2 Ann. d. Sci. Nat., ser. 5, t. xvii. 



