^^^^^H i II ITOMD.I-: 247 



of the class, from which they are inseparable, but there is 

 scarcely a group of Mollusca to which they are not allied. 

 The posterior termination of the rectum is not without ex- 

 ample ; it is essentially the same in Fissurella, and more or 

 less so in many of the Bullida and Pleurobranchida. M. Des- 

 hayes observes, that the want of eyes and tentacula has been 

 adduced as denoting affinity with the Annelida ; but, as we 

 have already observed, why not compare these deficiencies 

 with the Conchifera, their immediate predecessors ? And as 

 regards the Gasteropoda, the absence of eyes and tentacula is 

 not unusual : for instance, Bulla cylindracea has not a trace 

 of these organs; the Velutina otis of authors, Mr. Gray's 

 Otina, has" no tentacula; some of the BuUidce are without 

 eyes, and others without tentacula ; there are examples of the 

 Naticfe without eyes, and in the Dentalia both eyes and tenta- 

 cula are absent. Dentalium, in my method, is placed in the 

 van of the Gasteropoda, and Chiton follows ; both are closely 

 allied, and, we think, appropriately succeed the Conchifera. 



I do not say that, with the latter, the characters of alliance 

 are very decided ; still, on examination there will be found 

 analogies : for instance, in Chiton and Dentalium the branchiae 

 are placed symmetrically, though varying in particidar posi- 

 tion. In Chiton, though not in Dentalium, the anus has the 

 same posterior site as in the Conchifera and in some of the 

 patelloid forms. The strict sexual order of hermaphroditism 

 appears to obtain in both, and throughout the Patelloida to 

 the Pleurobranchidae and Bullidte, in which a more influential 

 plan of reproduction commences. These notes, in conjunction 

 with the special typical ones, only call for a very brief sum- 

 mary, and we think a calm review of all the circumstances 

 that are adduced will go far to convince zoologists that there 

 is not a locus standi for any organ in Chiton contrary to 

 molluscan essential characters ; all are confirmatory of the 

 Chitonidae belonging to that class, and the only return we can 

 make per contra is nil. 



It has been suggested by Professor Forbes in the e British 

 Mollusca/ vol. ii. p. 390, that an examination of the foetal 

 metamorphoses of the Chitons would throw light on their 



