ISOPODA. 15 



The crustaceous character of the mesosome is an exceedingly variable feature. 

 Usually the first four segments show it very clearly ; in the two following it is usually 

 concealed. The fourth segment frequently has a conspicuous and quadrangular space 

 in the mid-dorsal line, but as frequently this is quite absent. The succeeding segment 

 also bears evidence of a median division, but often it is only partly crustaceous. The 

 sixth segment is rarely crustaceous, but when it is the deposit is not evenly deposited. 

 This segment only'rarely exhibits the rounded postero-lateral margins so characteristic 

 of the ' Southern Cross ' species ; but here, on turning the animal on to the dorsal 

 surface, traces of the button-like process may be detected. 



Numerous specimens, male and female and all ages, were taken from the roots of 

 sponges inside the 25-fathom line. A few were taken at a time during the whole of 

 our stay in Winter Quarters. 



EUNEOGNATHIA. 



This genus was separated from the more widely-known genus Gnathia by the 

 Rev. T. R. R. Stebbing, on the ground that the first gnathopod of the male is 

 six-jointed, and that the pleopods have both branches fringed with long plumose hairs. 



EUNEOGNATHIA GIGAS. 



Anceus giyas Beddard (1), pp. 137-9. 

 Euneognathia gigas Stebbing (15), p. 338. 



Specific characters : 

 Male. 



Cephalosome short and broad, with a sinuous anterior margin and a short spur laterally. 

 Depressed in the centre and tuberculated externally. 

 Maxilliped with 4-jointed palp, setose externally. 

 Gnathopods G-jointed, with long setae externally, short ones internally. 



The single specimen measures some 16 mm. in length, the same size as the 

 Anceus gigas described by Mr. Beddard in the Isopoda of the ' Challenger ' Reports. 

 The following description will show that it must be identified with that species. 



The cephalosome is broad, rounded postero-laterally, and has a prominent spur 

 at the antero-lateral angle external to the antennae and just in front of the eyes. 

 The anterior margin is sinuous, due to fiue, small tubercular enlargements. The 

 middle one is the smallest, and is slightly indented. Its surface is rather depressed 

 anteriorly, but abreast and behind the eyes are two prominent tubercles on each side, 

 of which the posterior is much the larger, and this latter is separated by a smooth 

 narrow portion from the tumid posterior margin of the cephalosome. Mr. Beddard's 

 specimen is not satisfactorily figured. The anterior margin of the cephalosome is 

 similar to that of the ' Discovery ' specimen, but the tubercles are more exaggerated. 

 The ovoid lobes connected with the eyes do not exist as figured, but in place of them 

 are two prominent swellings, the surface of which is coarsely tuberculated. 



