18-4 THE VOYAGE OF H.M.S. CHALLENGER. 



both in form and in the structure of the petals according to age and sex, that I am quite 

 convinced it is impossible to define the Kerguelen specimens as a different species. One 

 of the specimens from Station 310 combines the features of the two sexes in having 

 nearly flush posterior ambulacral petals, while the anterior petals are almost as deeply 

 sunken as in well-developed females of the same size. 



Dr Studer also collected Hemiaster CGvclatus, Verrill, at Kerguelen Island, and 

 enumerates it as a distinct species in his list of Kerguelen Echinoderms (Berlin Akad. 

 Monatsb., July 1876, p. 457). He also speaks of finding the young in the cavity of the 

 external pouches of the petals of the large females. Mr Edgar Smith has also noted this 

 species in the Echinodermata of Kerguelen Island (Trans. Roy. Soc, 1879, vol. clxviii. 

 p. 272). 



From the evidence furnished by the large material collected by the Challenger, there 

 seems but little doubt the species which have thus far been distinguished as Hemiaster 

 australis, Hemiaster philippii, and Hemiaster cavernosus are aU different stages of 

 growth of one and the same species, but owing to the great difference in structure 

 between the ambulacral petals of the males and females, and the extraordinary changes 

 this species passes through from its youngest stage uutd it has reached its adult sexual 

 form, it was very natural that these several stages of growth should on scanty material 

 have been regarded as so many distinct species. 



The coloration of specimens from different localities appears also quite distinct, and in 

 some cases the test and spines are of a light brownish-yellow, in striking contrast to the 

 dark-coloured specimens found at other localities. 



Station 151. February 7, 1874. Off Heard Island. 75 fathoms; mud. 



Station 310. January 10, 1876. Lat. 51° 30' S., long. 74° 3' W. ; 400 fathoms; 

 bottom temperature, 7 '9° C; mud. 



Kerguelen Island, Betsy Cove. 15, 25 and 250 fathoms. 



Kerguelen Island. 10 to 100 fathoms. 



"Hemiaster gihhosus (PI. XX. figs. 5, 16, 22; PI. XXXIX. fig. 16). 



Hemiaster gibbosus, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 210. 



This is quite a large species, measuring 30 mm. in length. The outHne seen from 

 above is variable, in one case (PI. XX. fig. 5) it was nearly elliptical ; in another specimen 

 of about the same size, the posterior extremity was much the widest (PI. XX. fig. 6). 

 Seen in profile the test is vertically truncated at the posterior extremity, the apex is close 

 to the posterior edge, thence the test slopes gradually towards the anterior, somewhat 

 beyond the apical system. The anterior extremity is also abruptly truncated and rounded 

 towards the flat actinal surface. The posterior extremity of the actinal surface forms a 

 rounded keel, as is seen from the anal extremity (PI. XX. fig. 8). The outline seen facing 

 the anterior extremity is nearly globular. The small anal system is placed high upon the 



