iuf.dale: the chitons of thk. kermadec islands. 37 



The general coloration of the valves is cream, splaslied longitudinally, 

 but irregularly, with very pale orange, the girdle being uniformly 

 black. The whole shell seems less elevated and less sculptured, and 

 the girdle-scales are smaller, but I have decided to disregard these 

 points in view of the known variation of the common darker shells. 

 The internal coloration is whitish, the insertion-plates seem sliorter 

 and more delicate, whilst the slits are twelve in the anterior valve and 

 twelve or more in the posterior. The continual recuri'ence of this 

 peculiarly coloured shell suggests that in time this ' sport ' might 

 become fixed. The peculiar coloration met with in many species of 

 Ischnochiton and Chiton seems to support this theory. Length of type 

 14, breadth 8 mm. 



Hob. — Sunday Island, Kermadec Group. 



Station. — With /. hermadeceyisu. 



Family CHITONID^. 

 Genus Chiton. 

 Chiton, Linne, Syst. Nat., 10th ed., p. 667, 1758. 



Type (by monotypy !), Chiton tuberculatus, Linne. 



Four species only were included by Linne in his genus Chitoti, and 

 as three are unrecognizable the genus must be considered to be based 

 upon the second species only. Following Pilsbry, Australasian students 

 have referred various distinct styles of shell to the genus Chiton. In 

 the Mamml of Cuncliology, vol. xiv, p. 149, he wrote: "The most 

 natural primary division of Chiton is into two groups ; one to include 

 all American and some Old World species, in which the mucro is 

 anterior and the scales smooth ; the other to include Old World species 

 having the mucro subcentral and the scales striated. As this division 

 is based upon characters not always ea.sy to see, tlie following divisions 

 into sections is more convenient. 



Section Chiton (restricted). 

 Median valves having a single slit in each insertion-plate ; sinus 

 generally denticulate; scales closely imbricating. 



Section Radsia, Gray. 

 Median valves having two or more slits in each insertion-plate. 



Section Sclerochiton, Cpr. 



Median valves having a single slit in each insertion-plate ; teeth of 

 tail valve tending forward ; sinus smooth, scales of girdle separated." 



This arrangement appears to have been accepted without comment 

 until Thiele (Revision, p. 117) stated his conclusions thus: — 



" Genus Chiton, Linne. 



Section Radsia, Gray. 

 Sub-gen. Clathropleura, Tiberi. 

 Genus Sclerochiton, Cpr." 



When Pilsbry introduced Selerochitoti he wrote : " This section or 

 sub-genus represents a further development of the Acanthopleuroid 



