Mr. W. Clark 07i the Chitonidje. 281 



It has been suggested by Pi'ofessor Forbes in the 'British 

 MoUusca/ vol. ii. p. 390, that an examination of the foetal meta- 

 morphoses of the Chitons would throw light on their natural 

 position ; I propose, if practicable, to carry out this idea, though 

 the attempt will be attended with difficulties and uncertainties, 

 which need not now be alluded to. 



We are not sure that much will be gained by the investigation ; 

 it may possibly give us an idea of the affinities of remoter Imeages 

 with the present conditions of a particular genus or species ; but 

 we think the arrival of the animal, after its embryonic phases, at 

 an adult state, will not only give a knowledge of what it is not, 

 but of what it actually is, and more will be gained by a compa- 

 rative view of the mature organs with those of its allies. 



We apply these remarks to the present case, and think that 

 the oesophageal nervous collar, the buccal mass, the long spinous 

 tongue, the system of the circulation, and the true Gasteropodan 

 foot, will inform us that such an animal cannot be either one of 

 the Annelida or Cirripoda, or belong to any other group of the 

 Articulata, and we believe that the comparative examination of 

 the above-mentioned organs with those of the Conchifera and 

 Patelloida will irresistibly lead us to acknowledge their true 

 molluscan composition. 



Chitonid.e. 



The British Chitons are a group of about ten species ; we have 

 given notes of three, selecting the C. fascicularis as the type. 

 They inhabit all the zones according to their respective special 

 habits. As regards Bi'itish geographical distribution, they appear 

 to arrive at larger growth in the northern latitudes. 



Chiton, Linnfeus. 

 C. fascicularis, Linnaeus et Auct. 



Animal forming an elongated oval, the body being convex on 

 the upper surface, and enveloped in a mantle, thin above, but 

 gradually resolving into a thick, strong, broad, granular margin, 

 clothed with a rigid setose white fringe, and on each side is 

 furnished with eight packets of yellowish white bristles, 12-15 

 in each, and two of the same number at the anterior end ; above 

 these are imbedded, in the margin and longitudinal area of the 

 animal, eight transverse, convex, saddle-shaped, beaked, imbri- 

 cated, strongly shagreened, dark gray testaceous plates, whereof 

 the anterior one has five emarginations, the six behind in succes- 

 sion one on each side and two on the terminal margin of the 

 eighth. The head is a membranous puckered frill, under which 

 is the rugosely-rayed buccal disk with its round orifice in the 



Ann. ^ Mag. N.'Hist. Ser. 2. Vol. xi. 19 



