38 PROCKEDINGS OF THE M ALACOLOGICAT, SOCIKTY. 



cliaracters which some Australasian species of the restricted genus 

 Chiton assume. In Ch. pellis-serpentis, for example, the macro is 

 median, the posterior teeth tend forward somewliat, the sinus is 

 smooth or only very obsoletely denticuhate, and the girdle-scales are 

 striated and rather separated. In Sclerochiton the mucro is slightly 

 more posterior, the teeth slightly more tilted forward; the sinus is 

 smooth, and the girdle-scales still more separated. Ch. pellis-serpentis 

 could be placed almost as well in Sclerochiton as in Chiton s.s. ; the 

 necessity of reducing Sclerochiton to the rank of a section under 

 Chiton will therefore be apparent." It must be remembered that 

 Pilsbry was only conversant with Sclerochitoti from a study of 

 Carpenter's notes and figures. Since his time the genus has become 

 fairlv well known, and the species have never been confused with 

 Chiton. Sclerochiton is nearly allied to Acanthopleura and Liolophura. 

 In New Zealand the two commonest Chitons are Ch. j)eUis.%erpenfis, 

 Quoy & Gaimard, and Ch. quoyi, Dc^hayes ' ; two more dissimilar 

 species, as referable to the same genus, can scaicely be imagined. 

 A third Chiton I not uncommonly obtained was Ch. areus, Keeve. 

 Three distinct types of shell seemed confused under one generic name. 



At the Kermadecs I found two species of ' Chiton ' which greatly 

 differed ; one recalling Ch. pellis-serpentis, Quoy & Gaimard, the other 

 vaguely resembling Ch. cereus, Reeve. Critical examination proves 

 their onlv resemblance to be the possession of a scaly girdle, and that 

 the teeth of the insertion -plates are pectinated, but in this latter 

 character they are very different. The dissection of many species of 

 ' Chiton ' provided much of interest with regard to many details of 

 their structure, and one point worthy of consideration in the present 

 place (I purpose to deal in much detail in this matter elsewhei'e) is 

 the number of slits in the anterior insertion-plate. When Pilsbry 

 was discussing Plaxiphora (Man. Conch., vol. xiv, p. 313, 1893) he 

 wrote: "It must be understood that although in many groups of 

 Chitons, such as all Ischnochitoninse and Chitoninse, the number 

 of anterior slits is a character of merely specific importance, the case 

 is far otherwise in those groups in wliich the slits correspond in 

 number and position with external ribs such as Nuttallina and its 

 allies, and the Mopaliidte, Acanthochitidaj, etc. In these groups the 

 number of slits in the anterior insertion-plate is a highly constant 

 generic character, apparent exceptions being readily traceable to the 

 splitting of one or more primary teeth." 



I now suggest tbat when the genera ' Chiton^ and ' Ischnochifon' 

 are better known, the slitting of the anterior insertion-plate will be 

 found of as much importance as in the genera Pilsbry named. The 

 species similar to Ch. cereus, Reeve, have been separated by Thiele as 

 a sub-genus of Chiton, his conclusions being based on anatomical stud}-. 



^ The correct name of this species is Amaurochitoii glaiicus, Gray (Spicilegia 

 Zoologica, pt. i, p. 5, 1828) : this name was rejected by Pilsbry as he 

 conckKled the description was inadequate and the type lost. I find the 

 type is preserved in tlie British Museum, and, moreover, that it was 

 recognized by Carpenter as weU as other investigators, notes to this effect 

 being inscribed upon the back of the type tablet. 



