REPORT ON ZOOLOGY. 223 



bigny has been adopted by Rang in his Manuel des Mollusques 

 already alluded to. 



2. Pteropoda. — De Ferussac has given a systematic arrange- 

 ment of this class in the Bull, des Sci. Nat. for 1827 *. Rang 

 has made several important additions to it, as well as recorded 

 many valuable observations respecting genera and species which 

 were already known. Nevertheless we have still but an imper- 

 fect knowledge of this group. 



3. Gasteropoda. — This being the typical and the most exten- 

 sive class among the Mollusca, it has received more general 

 attention than any of the others. Many of the families and ge- 

 nera contained in it have been made the subject of valuable 

 monographs by different individuals, which, however, it would 

 lead too much into detail to allude to more particularly. Na- 

 turalists do not appear to be agreed as to the exact value of cha- 

 racters derived from the shell in distinguishing the genera of 

 this class. M. Deshayes, in a paper in the Ann. des Sci. 

 Nat. for 1831 f, has recoi'ded some anatomical details, which 

 would seem to have been undertaken with the view of throwing 

 some light on this matter in the case of the Helices. His ob- 

 ject is to discover whether there may not be found some pecu- 

 liarity in the internal structure of the animal sufficient to war- 

 rant the adoption of many genera in this family, which hav- 

 ing been established solely upon the characters of the shell, have 

 not hitherto been received by all naturalists. T am not aware, 

 however, that he has carried on this investigation beyond the 

 case of Draparnaud's genus Succinea, which is the only one 

 treated of in the above paper. 



The opercle of shells, which, as already stated, has been much 

 employed by Mr. Gray in his arrangement of the Gasteropoda, 

 has been since studied with great care by Blainville, who in a 

 memoir in the Bull, de la Soc. Philom. for 1825 +, proposes 

 to adopt characters derived not merely from the presence or ab- 

 sence of this part, but from its form and structure, its position, 

 and mode of attachment to the animal. In the Ann. des Sci. 

 for 1829 §, Duges has also a paper on this subject. His prin- 

 cipal object is to trace the analogies between this part and the 

 upper valve of the Inaequivalve Acephala, more particularly as 

 respects its mode of growth, and the production of the striae on 



of the Testaceous genera into two groups, characterized by the presence or 

 absence of a siphon. I believe De Haan was the first to make use of this cha- 

 racter, although D'Orbigny is said to have had recourse to it without any know- 

 ledge of De Haan's work. See Diet. Class. d'Hkt. Nat., torn. xi. p. 56. « 



• torn. xii. p. 345. f torn. xxii. p. 345. J pp. 91 and 108. 



^ tuiji. xviii. p. 113. 



