120 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
the Lymneana, and are, indeed, more closely allied to some of the marine 
families of Gasteropoda—the Turbinacea, the Canalifera, or the Purpuri- 
fera: we place them, however, at the commencement of the Pectini- 
branchiate series, in order that the fluviatile water-breathing kinds may 
immediately follow the fluviatile air-breathing kinds ; a decided and im- 
portant change of habit, which always imparts a distinct peculiarity of 
character to the shell, as well as a corresponding variation in the orga- 
nization of its inhabitant. We are aware that this distribution of the 
Melaniana, introduced by Lamarck, is opposed both to that of Gray and 
De Blainville ; still, as we have endeavoured to establish the propriety of 
separating the marine from the terrestrial mollusks, so shall we attempt 
to show, that the same measure of distribution may be profitably observed 
in separating the marine kinds from the fluviatile. The Melanie are un- 
doubtedly allied to the Cerithia, even in their habits, because many of 
them, distinguished by some authors with the title of Potamis, are found 
located in brackish water at the mouths of estuaries, or at the confluence 
of rivers with the sea. The Cerithia, however, cannot consistently be 
separated from the Canalifera, and this is an embarrassment which readily 
accounts for the different situations that the Melaniana have been assigned 
to by different authors. The two genera which are included in this 
family are referred by De Blainville to distant parts of the class: the one, 
Melania, to his family of Ellipsostomata, together with Rissoa and Phasi- 
anella ; the other, Melanopsis, to his family of Entomostomata, in company 
with Cerithium and Planavis. De Montford again places the genus Mela- 
nopsis between Achatina and Terebra ; whilst it is arranged by his disciple 
Gray in the same family with the genera Scalaria, Turritella and Sola- 
rium \* 
* The family Littorinide of Gray does certainly not exhibit that peculiar accuracy of di- 
stinction which usually characterizes the families of this ingenious author: it appears, indeed, 
to be made up of the rejectamenta of the class, for no less than fifty-five genera are assigned 
to it, of the most anomalous character. Are the Paludestrine, for example, rightly placed in 
this family? Are they more closely allied to the Scalarie or the Solaria than to the Palu- 
dine? ‘They are freshwater mollusks, and differ from these last only in having their eyes 
situated at the base of the tentacles instead of at the summit; the genus therefore, if adopted 
at all, should most assuredly be referred to his family of the Paludinide. 
