ISOPODA. 25 



conical tubercle (Studer, Beddard), a rounded tubercle ('Discovery'), or as Eights 

 words it the entire space is elevated to form " somewhat the figure of a corona in high 

 relief." The description and figure are not too explicit, but it does not appear to be ;i 

 matter of vital importance. Dr. Studer further points out that the median ridge of the 

 caudal shield bears three teeth only, the first of which is the largest. Ili.s figure from 

 its great breadth is probably that of a female. 



Mr. Beddard gives much better figures of this species, and increases the number 

 of teeth on the keel of the caudal shield from three to six. 



From the sizes of the specimens obtained in these collections it would appear that 

 the greater number are not adult. Eights' specimen, as figured, unquestionably is so ; 

 the larger ' Discovery ' specimen is approaching that condition. In reply to an enquiry, 

 my friend, Dr. Caiman, confirms my suspicion that the ' Challenger ' specimens are not 

 adult, the largest female, which has been partially dissected, bears traces of having had 

 oostegites, in the others they are quite rudimentary. None of the males have the 

 third thoracic appendage modified. 



The sternum is quite smooth, that of the first thoracic segment which bears the 

 maxillipeds is narrow and enclosed by the succeeding one. It projects forwards in a 

 conical manner between the maxillipeds and bears a median ridge. The second passes 

 completely across the body, the epimera being separated by a groove. 



In the middle line the median keel of the preceding segment is continued through 

 half its length, where it widens out and disappears ; behind this is a groove which 

 forms the anterior boundary of a lip-like structure rather more than 5 mm. w y ide. 

 The three following segments are conspicuously divided in the middle line, the 

 remainder less distinctly so. The sixth is only indistinctly separated from the 

 following, while the seventh and eighth are fused. 



The posterior border of the first three abdominal segments is, in the middle line, 

 produced backwards into a spine. Small in the first, it is but little larger in the 

 second, but in the third it is very much larger. This feature is alluded to by 

 Mr. Beddard as a sexual character, but one which is not constant in all species. For 

 this particular species it is not alluded to either by him or Dr. Studer, and Eights' 

 figure is not satisfactory in this respect. AVhat I take to be the genital apertures 

 are two small ovoid slits near the posterior border of the last thoracic segment and 

 some little distance from the middle line. Mr. Beddard states that these apertures 

 are invariably circular in the male, but neither he nor Dr. Studer allude to them for 

 this species. Eights is equally silent on this point. 



The first antennae rise in a depression of the anterior margin of the ccphalosome, 

 and are directed outwards. Each consists of a tapering four-jointed peduncle, the 

 proportions of these joints being 3. 5. 4. 2'5, and they are followed by a multi- 

 articulate flagellum. 



Dr. Studer states that the flagellum has twenty-two joints, Mr. Beddard states 

 twenty-five. In all the ' Discovery ' specimens the flagellum, although injured, 



VOL. V. I, 





