REPORT ON THE POLYPLACOPHORA. 29 



accurately corresponds with specimen C. in the above tables. I have no hesitation in 

 identifying CJiiton granulatus, Gmel., with the Acanthopleura which appears to be so 

 common at the Barbadoes (A. and B.,ante) ; and it is equally probable that Chiton piceus, 

 Gmel., is identical with my specimen C. I feel some hesitation in retaining that name 

 for it ; as, judging from its geographical distribution, Gmelin's form would include two 

 distinct species. Blainville, however (Diet, des Sci. Nat., vol. xxxvi.), gives only the 

 American locality, and, as has been above noted, the Red Sea species differs from any 

 West Indian form. 



Blainville 1 gives Gmelin's two species, and describes on p. 544 a new species, CJiiton 

 convexus, which is of very doubtful value. 



Sowerby gives the following synonymy for CJiiton piceus in the Conch. Illust., p. 1 : — 

 " CJiiton convexus, CJiiton granulatus, CJiiton gemmatus, Chiton tuherculatus, CJiiton 

 unguiculatus, CJiiton zonatus (auctorum) ; " these are all Blainville's species (loc. cit.). 

 Reeve 2 follows Sowerby in the synonymy, but it is not clear what species he intends, as 

 in the Conchologia Iconica 3 AcantJiopleura spiniger is referred to as Chiton piceus. 

 Gray 4 refers to this species as " Maugeria picea, West Indies." 



Reeve describes AcantJiopleura occidentalis from the West Indies, 5 which is probably 

 one of these two forms. 



AcantJiopleura spiniger and its varieties can now be distinguished from the other 

 species without much difficulty. 



The posterior valves alone separate AcantJiopleura incana from all the preceding. 

 The Japanese and Australian specimens of this form appear to have well-marked differ- 

 ences. It can only be decided after an examination of a greater number of specimens 

 than I have studied, and of examples from intermediate localities, whether these distinc- 

 tions are to be considered as specific or varietal. In the former case Gould's name must 

 be retained for the Australian form, — he describes the interior of the shell as being " red 

 and violet, somewhat iridescent," and certainly the madder- brown and pinkish colour of 

 my specimens offers a marked contrast to the uniform black or blackish brown of the 

 Japanese specimens. The laminae of insertion are relatively smaller in the Australian 

 form, and the sculpture of the shell appears to differ slightly, but my specimens are 

 considerably eroded. 



Except for the colour of the under surface, the posterior valve of AcantJiopleura 

 incana very closely resembles that of EuplacipJwra petholata, Sow., also from South 

 Australia. There may be some connection between the two forms, but the character of 

 the insertion plates and the nature of the girdle sufficiently separate the two genera. It 

 should not be forgotten that Carpenter divides the whole group of Chitons into Regular 

 and Irregular, basing his classification upon the dissimilarity between the anterior and 



1 Diet, des Sci. Nat., 1825, vol. xxxvi. p. 545. 2 Conch. Syst., 1842, p. 11. 



3 1847, pi. xiii. fig. 70. 4 Guide Moll., 1857, p. 184. 5 Conch. Icon., 1847, pL xix. fig. 76. 



