CRUSTACEA FROM THE ' CHALLENGER ' EXPEDITION. 25 



details on the structure of both sexes, which could only be discovered when it was 

 possible to dissect one of the specimens. I now have to publish some figures which 

 could not be given in my first paper, and add a few words to them. But before doing 

 this, I must declare that the name of Thaumops peUucida must be withdrawn, as this 

 animal has been already described under the name of Cystisoma Neptunus by Guerin- 

 Meneville*, from a single specimen caught in the Indian ocean. I see this from Spence 

 Bate's ' Catalogue of Amphipodous Crustacea ' f , which I have just received, and which 

 contains a copy of Guerin-Meneville's rather bad figure and a short description of a 

 specimen, which probably is a male. 



Guerin-Meneville (and Spence Bate ?) regards Cystisoma as belonging to the Hyperidae 

 family, and takes the antennae (which are in front of the head) as representing the 

 second pair. Why they should be homologous with these I do not know ; nor do I think 

 they are ; for in Phronimids, Oxycephalids, and Hyperids the second antennae have a 

 funiculus consisting of several (more than two) joints. Now in Cystisoma the antennte 

 have got two joints, which seem to represent the one a funiculus joint, and the other the 

 fiageHum of the first antennae of Phronima. 



Against a union of Cystisoma with the Hyperids may be advanced, besides the form 

 of the head (which is more Typhid-like) and the absence of the second antennae in both 

 sexes, the absence of a palpus on its mandible (PL XL fig. 6). The palpus is always 

 present, according to Glaus, in Hyperids, but is wanting in Phronimids. Besides, there 

 are so many peculiarities distinguishing Cystisoma, which I have enumerated in mv 

 above-mentioned paper, that I do not think it possible to keep it in one of the hitherto 

 received families, but that now, when we know its structure better, we have to establish 

 for it a special family called Cystisomidae. 



The first maxilla has been described, and is now figured in PL XI. fig. 7. The second 

 maxilla could not be found, and is probably represented by an organ which might have 

 arisen from the union of the second maxillae and the under lip (PL XL fig. 8). This 

 organ (I) is attached to the third joint of the reduced maxillipedes, and surely acts phy- 

 siologically as an under lip. The maxillipedes are reduced and fused together so as to 

 form one organ consisting of two basal joints and two claws (fig. 8, m), between which is 

 attached the organ which we suppose to represent the maxillse and the under lip. 



The male differs by the absence of glands at the top of nearly all the appendages, 

 especially in the last pair of pereiopoda, which, according to this, have not the same 

 clumsy appearance as in the female. The two testes begin just behind the stomach 

 (fig. 5, t), and send vasa deferentia to the last segment of the pereion, where two simple 

 genital openings are to be seen between the last pair of legs (fig. 5, a g). 



Probably (as in Phronima) the full-grown male is somewhat smaller than the female, 

 it seems that Cystisoma Neptunus can attain a very considerable size ; for the last 

 and largest male which we got in the trawl has a length of 103 millims. It seems 

 that these oceanic amphipods have a very wide geographical distribution. Cystisoma, 

 as we have seen, was first described from the Indian Ocean ; and Oxycephalies piscaior is 



* Guerin-Meneville, in Revue Zoologique, July 1842, p, 214. t Page 311, pi. 1. fig. 7. 



SECOND SERIES. — ZOOLOGY, VOL. I. E 



