CLASSIFICATION. 13 



the Gastrochanidce, though, by the teeth, it is allied to the 

 VenereSj but we consider the character of the teeth of very 

 inferior value to the closed mantle, which points out its natural 

 position. Teredo terminates the Acephala and passes them to 

 the Dentaliadae, our primary family of the Gasteropoda, agree- 

 ably to the indices that are pointed out in the last page of the 

 anatomy of Teredo. 



Third Division. 



TLATERIBRANCHIATA. 

 GASTEROPODA < CYCLOBRANCHIATA. 

 LCERVICOBRANCHIATA. 



The animals of this division are strict hermaphrodites with- 

 out congression. The Dentaliada are the Lateribranchiata of 

 the synopsis, of which family I have already given in the 

 ' Annals of Natural History ' a detailed anatomy ; they have 

 claims which appear not to be ill-founded, to stand as the first 

 family of the Gasteropoda, from the connection between them, 

 by the position of the branchiae, with Teredo, the last family of 

 the Acephala. The Chitons are the Cyclobranchiata. The 

 Patella, Acmaea, Pileopsis, and Calyptraea are the Cervico- 

 branchiate patelloid forms with a single non-symmetrical 

 branchial plume; and Fissurella, Emarginula, Puncturella, and 

 Haliotis are in the same Cervicobranchiate category, but 

 differ from the first patelloid group in having two symmetrical 

 branchial leaves. 



Fourth Division. 



{CRYPTIBRANCHIATA. 

 PLEUROBRANCHIATA. 

 PULMONIFERA. 

 PARS-PECTINIBRANCHIATA. 



In this division there is an important advance in sexual 

 arrangement ; pure hermaphroditism is abandoned, and that of 

 mutual congression has succeeded. The families are the Pleu- 

 robranchida, Aplysiada, Bullidte, Pulmonifera, Pteropodida, 



