DENTALIAD^E. 225 



GASTEROPODA. 



That this division of the Mollusca is the sequence of the 

 Bivalves is universally acknowledged ; this is shown by a body 

 of facts that are familiar to all who cultivate this branch of 

 science ; but it is also evident that the Gasteropoda have very 

 decided marks of an advancement to superior organization ; 

 the distinct head, eyes, tentacula, denticular apparatus, the 

 oesophagean concentration of the medullary ganglions, the 

 character of the foot, the almost invariable state of freedom 

 and consequent increased facility of locomotion, together with 

 a greater complexity of the generative developments of many 

 of the families, are sufficient proofs of a great progress in 

 animalization. 



It is not necessary here to enter on anatomical remarks, as 

 almost every point connected both with the internal and ex- 

 ternal animal structure is again and again mentioned in the 

 observations concerning the different families ; it would there- 

 fore be a useless repetition to extend our notes in this 

 direction, and we at once proceed to introduce the respective 

 families, only premising that there are still some gaps in the 

 descriptions of the animals, but these deficiencies are daily 

 disappearing in consequence of many recent discoveries. 



DENTALIAim 



We are obliged to provide for this family of one genus, 

 a distinct branchial section, which, from the symmetrical 

 lateral disposition of the branchiae, we have termed Lateri- 

 branchiata-, we consider this arrangement subject to our 

 determination of the branchiae being confirmed. Large ana- 

 tomical details of the Dentalium Tarentinum are annexed. 



From my observations in the ' Annals of Natural History/ 



Q 



