390 CHITONID^. 



as members of their special province. Cuvier held them 

 to be gasteropods closely allied to Patella Avith which 

 genus he associated them to form his sub-order Cyclo- 

 hranclies. De Blainville, on the other hand, considered 

 them as more nearly allied to Annellida than to mollusca, 

 and constituted a special group Polyplaxi'phoTa for them. 

 Unlike any other mollusks their bodies are protected by a 

 series of shelly plates, resembling so many articulations. 

 Their organs of reproduction are symmetrical, and re- 

 peated on each side of the medial line, and there are 

 a pair of sexual orifices. Their circulation is peculiar ; 

 the heart resembles the dorsal vessel of an annellide. On 

 the other hand, their respiratory organs are very similar 

 to those of Patella^ their digestive system and lingual 

 apparatus remind us of those of Prosobranchiate mollusks, 

 and the creeping disk is that of a true Gasteropod. As 

 our knowledge stands at present, we prefer to regard them 

 as an abnormal family of Prosobranchiata, and trust, 

 before long, that some active observer resident by the 

 coast will occupy himself with studying the development 

 of the Chitons, and endeavour to ascertain the form they 

 assume in their larval condition. Whoever does so will 

 make an important discovery, and do more towards fixing 

 the true position of these anomalous creatures than all 

 cabinet examinations of them have yet enabled us to effect. 

 In a recently published paper by Mr. J. E. Gray, the 

 Chitons are maintained to be " normal Gasteropods, with 

 a series of more or less rudimentary valves in front of the 

 usual shell." He considers the posterior terminal valve to 

 be the homologue of the shell of Patella. 



