63 



May 11, 1847. 

 William Spence, Esq., F.R.S., in the Chair. 

 The folio \ving paper was communicated to the Meeting : — 



On the Genera of the Family Chitonid^. By J. E. Geay, 

 EsQ., F.R.S., F.Z.S. ETc. 



This family now contains so many species, oflFering such varied 

 modifications of form and structure, that it becomes necessary to 

 separate it into several genera, for the purpose of more accurately 

 determining the species and showing their relations to each other. 



Most authors have regarded the family as a single genus, and even 

 M. De Blainville, who formed the family into a class under the name 

 of Polyplakiphora, so regarded them. He forms of this class and his 

 Nematopodes or Barnacles a subtype of the animal kingdom, w'hich 

 he called Malentozoaria or Molluscarticulata ; but there is no suf- 

 ficient character to separate the Chitons from the other MoUusca, 

 and the Nematopodes are now kno-wn to be Crustacea, so that this 

 division or subtype of the animal kingdom has been erased from the 

 system by most succeeding authors. 



Dr. Leach in his MSS. proposed to divide this family into genera, 

 according to the form of the appendages which cover the upper sur- 

 face of the mantle ; and Risso, \vho was in constant correspondence 

 with Dr. Leach, has in his work published two of Dr. Leach's genera. 

 Mr. Guilding has formed some genera on the šame principles in the 

 Zoological Journal, and I have added two others in the Synopsis of 

 the British Museum for 1841. 



I may remark that these appendages of the mantle form exceedmg 

 good characters for the more minute di\ision of the groups, but the 

 scales so gradually pass into spines or tubercles on the one side, and on 

 the other they so gradually diminish in thickness to furfuraceous 

 scales, \vhich are easily deciduous that it is difBcult to define when they 

 are quite absent ; therefore they do not afford characters of suflScient 

 importance to use them as Leach, Risso and Guilding have done, for 

 the primary divisions of the family. 



Lamarck divided the family into two genera, Chiton and Chitonellus, 

 but he left in the former genus several species -vvhich are more natu- 

 rally allied to the latter. 



M. De Blainville in 1825 published a monograph of the family, 

 under the article ' Oscabrion' in the Dict. Sci. Nat. xxxvi., in vi^hich 

 he introduced some new characters for the division of the species into 

 sections. He observes : " Les organes sur lesąuels nous appellerons 

 successivement Tattention pour le distinctlon des espėces sont les 

 suivants : — *• 



"1. L'existence ou I'absence des pairęs de pinceau de soies dis- 



