42 PUOCKEDINGS OF THE MALACOLOGICAL SOCIETY'. 



The above description is drawn up from a normal specimen selected 

 as type. Some specimens are almost keeled, with fewer sulci, less 

 slantinj;;, on the pleural areas, whilst sometimes the anterior valve- 

 raying lacks nodulosity altogether, and in other cases it is well 

 pronounced. A very juvenile specimen, 5 mm. long, is smooth 

 throughout, the surface minutely quiucuncially granulose. It recalls 

 Chiton tranHlucena, Hedley & Hull. Specimens, 6"5 to 7 mm. long, 

 are still smooth, but there now appear live or six sulci on the pleural 

 areas. In some concentric growth-lines can be observed. These 

 suggest the Ch. jugosiis, Gould, group, especially Ch. tom'anus, 

 Hedley & Hull. An older shell, though only 6mm. long, shows 

 the ribbing on the anterior valve to commence on the outside, fourteen 

 being counted, which extend less than one-third the distance to the 

 apex ; the lateral areas are more strongly marked than in the preceding 

 stage, a slight depression indicating the differentiation into ribbing ; 

 at the edge of the posterior valve nine nodules mark the beginning of 

 the radial ribs ; the pleural areas are sculptured with six clean-cut 

 sulci, which extend across the valve. Specimens, 10 mm. long, in 

 some cases show little advancement on the previous stage, whilst 

 in others thej^ show almost perfectly developed adult sculpture. 

 Length of type 18, breadth 10"5 mm. 



JIab. — Sunday Island, Kermadec Group. 



Station. — On the underside of clean, smooth stones below low tides. 



"On sraootli stones just below low-water lived species of Chiton, 

 of the cereus, Ileeve, group. ... I have written species as I have so 

 far failed to realize how many or how few I have collected. The 

 shells can be separated into tbree forms of Chiton. ... If these 

 forms could be classed as variations of one species, that would seem 

 best, but then we are confronted with the fact that C. cereus, Reeve, 

 and its rehitions are very constant. . . . Then how should a species 

 of such group commence varying under such restricted conditions as 

 is offered them on such a small area. These forms were all living 

 under absolutely the same conditions, so that I have been forced to 

 suggest that they present convergence of species through the action 

 of identical external conditions." 



Somewhat against my will 1 here admit only one form, as though 

 when collecting differences easily observable were noted, the dried 

 shells show to me at present no constant characters whereby forms 

 can be diagnosed. Under the heading Ch. corypheuH, Hedley and 

 Hull, from Norfolk Island, the authors write: "This shell appears 

 to approach C. di&color, Souverbie, of New Caledonia, but differs 

 from that species in the fewer radial ribs on the end valves, and the 

 fewer and less anteriorly prolonged sulci in the central areas. Chiton 

 canalicidatus, Quoy & Gaimard, from New Zealand, is also related, 

 but is more elevated, and sharper keeled, and has a harslier sculpture. 

 A similar, if not identical, species was found by Mr. T. Iredale on 

 llaoul or Sunday Island, Kermadec Group." I fully agree with the 

 relationship of Ch. corypheus, Hedley & Hull, with Ch. discolor, 

 Souverbie, but cannot see any close resemblance in that species to 

 Ch. canalicidatus, Quoy & Gaimard, whereas it has a great likeness to 



