REPOET ON THE ISOPODA. 147 



typical Sphserorna ; it must be remembered, however, that Sphseroma (Isocladus) differs 

 from Cilicsea in that the dorsal spine is developed from the terminal segment of the 

 thorax, while in Cilicsea it is an outgrowth of the abdomen ; hence, there is no possi- 

 bility of confounding these genera, although, on a superficial view, the similarity is great. 



There are no reasons at present for supposing that all the species of the genera 

 Cymoclocea and Splissroma exhibit this sexual dimorphism — in fact Sphseroma gigas 

 certainly does not ; but this is no reason for separating generically those forms with a 

 well-marked sexual dimorphism from those without any great sexual differences, unless 

 we have here a case of protective mimicry analogous to that exemplified in many 

 Butterflies ; for the present, therefore, it appears to me to be necessary to regard 

 Cymoclocea, Nessea and Cilicsea as synonymous ; I shall describe a new species under 

 the generic title of Cymoclocea. 



The family Sphseromida? is almost universally distributed, and is according to 

 Gerstaecker more specially characteristic of the temperate regions, though found 

 sparingly everywhere else. It is pre-eminently a shallow-water family, only one species, 

 Cymoclocea abyssorum, being found in the great depths of the ocean. It is interesting to 

 note that in this species there are certain structural peculiarities analogous to those 

 exhibited by Bathynomus and Anuropus (see p. 152), which may perhaps be the result 

 of the habitat ; the fourth and fifth pairs of abdominal limbs are in all Sjjhseromidee 

 modified into respiratory organs, the endopodite taking on this function more particularly, 

 while the exopodite remains thin and membranous and serves as an operculum ; in 

 Cymoclocea abyssorum both endopodite and exopodite are respiratory in structure, having 

 the form of complicated folded plates. . This fact, however, perhaps loses a good deal of 

 its significance since exactly the same condition is met with in Amplioroiclea, while 

 Anuropus has no shallow-water allies in which there is a similar hypertrophy of the 

 respiratory lamella?. In Amplioroiclea typica the fourth and fifth pairs of abdominal 

 appendages are described and figured by Milne-Edwards as being exactly similar in 

 structure to the one of Cymoclocea abyssorum, and in Amplioroiclea falcifer, 1 from New 

 Zealand, I have myself observed precisely the same modification of their structure. 



The eyes of Cymoclocea abyssorum are white in colour, owing to a complete absence 

 of pigment, a character frequently met with in deep-sea Isopoda. 



Ceratocephalus, White, MS. 



Ceratocephalus, White, MS., Woodward, Art. Crustacea, Encycl. Brit., ed. 9, p. 659. 

 Bregmocerella, Haswell, Proc. Linn. Soc. N.S.W., vol. ix. p. 1004. 



This genus of Spheerorniche has been described almost simultaneously by two different 

 writers. Dr. Woodward, in his article Crustacea, published in the 9th edition of the 



1 A species kindly forwarded to me by Mr G. M. Thomson. 



