152 SUBANTARCTIC ISLANDS OF NEW ZEALAND. [HoUithurians. 



The spicules of the body-wall consist of wheels and hooks (signiata). The 

 wheels (figs. 3o, 36) are few in number and of small size, sparingly scattered in the 

 integument. In the larger specimen they measure about 0*053 mm. in diameter. 

 In the smaller specimen, after much searching. I was only able to find a single wheel 

 (fig. 3e), but this was slightly larger, about 0-067 mm. in diameter. The wheels 

 agree in structure with those of C. dunedinensis, but the crenation or dentation 

 of the inner edge of the rim is relatively much coarser. There is, at any rate 

 sometimes, as in C dunedinensis, a round hole in the middle of the face of the 

 wheel opposite to the 6-rayed cross (fig. 3e). The wheel in C. dunedinensis, 

 however, is very much larger than in C. benhami — about 0-16 mm. in diameter 

 (c/. fig. 4a). 



The hooks, or sigmata, closely resemble those of C. dunedinensis, and are of about 

 the same size — about 0-11 mm. from bend to bend (figs. 3c, 3d, 3/, 3g). 



The tentacles are supported by rather slender curved rods, up to about 0-06 mm. 

 in length, with once or twice dichotomously branched ends (figs. 3/*, 3k, 31). Similar 

 spicules occur in C. dunedinensis, though not hitherto noted. 



Remarks. 



This species is of interest as showing clearly the impossibility of basing generic 

 distinctions merely upon the arrangement or even upon the presence or absence 

 of the wheels. In this respect, with its scarce and feebly developed wheels, it is 

 intermediate between C. dunedinensis and C. geminifera, Dendy and Hindle, in 

 which the wheels have completely disappeared, while in Rhnhdomolgus novae-zea- 

 landiae, Dendy and Hindle, not only the wheels but also the sigmata, or hook 

 spicules, have disappeared.* 



C. dunedinensis, C. henhami, and C. geminifera are all very closely related to 

 one another, and the following comparative notes may be of service in distinguishing 

 them : — 



C. benhami appears to attain a considerably larger size than C. dunedinensis, but 

 the tentacles are relatively, if not absolutely, smaller, and the digits do not increase 

 gradually in size from base to apex, the terminal pair being considerably larger 

 than any of the others. In C. dunedinensis the diameter of the wheels, though 

 variable, may be more than twice that of the wheels in C. henhami, and the inner 

 margin of the rim is much more finely toothed, especially in proportion to the size 

 (c/. figs. 3a, 36, 3e, and 4a). 



C. geminifera differs from both the foregoing in the complete absence of wheels, 

 and also in the much smaller size of the hooks. These spicules were, unfortu- 

 nately, at first wrongly described and figured,t the material having apparently 

 been accidentally subjected to the action of some acid, whereby the spicules 

 had become corroded and quite altered in character. This mistake has already 

 been rectified,J but the spicules are now for the first time correctly figured 

 (figs 5a-5c). 



* Dendy and Hindle, Linn. Soc. Jour., Zool., vol. xxx, p. 113, 1907. 

 t Loc. cU., p. 112. 



j Dendy, " Note on the Spicules of Chirodota geminifera Dendy and Hindle," Linn. Soc. Jour. 

 Zool., vol. xxx, p. 251, 1908. 



