136 CLASS III]. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
Pl. CXCIX. Fig. 12. 
NAVICELLA SUBORBICULARIS, Sowerby, Appendix to Tankerville Cata- 
logue, p. 10. Recluz, Revue Zoologique Soc. Cuv., 1841, p. 378. 
NERITINA, Lamarck. 
Testa tenuis, subglobosa, epidermide olivacea induta; spira indistincta, 
interdum feré obsoleta, anfractibus interdum spinis cavis ornatis ; 
apertura semirotunda ; columella planulata, effusa; labro simplici, 
interdum utrinque latissimé dilatato. Operculum testaceum, semi- 
ovatum, appendice laterali, acuto, instructum. 
Lamarck’s method of separating the freshwater mollusks from those 
that are marine, a plan which he judiciously adopted in all cases where 
it may be carried out with tolerable accuracy, and without injury to the 
system, suggested to him the formation of the present genus. Before his 
time the Neritinz were not elevated to the rank which is now commonly 
assigned to them, but merely distinguished as ‘‘ the freshwater Nerites,” 
in a section of the genus Nerita; the difference between the habits of the 
Nerite and Neritine is, however, so faithfully indicated by the compo- 
sition and general appearance of their shells, that, with all deference to 
the views of so excellent a conchologist as Deshayes, we think the di- 
stinction ought not to be abandoned. ‘The Neritinze have much thinner 
shells than the Nerite, and they differ in being always covered with an 
epidermis ; another distinguishing character is, that the margin of the 
aperture is never crenulated. The Neritine notwithstanding seem to 
possess a vast modification of habit, for, like some other aquatic mol- 
lusks, they appear to have the faculty of living for a considerable time 
out of water: an instance is recorded by Lesson of his finding the Neri- 
tine upon the branches of trees planted at some little distance from the 
river side; and Cuming informs us that he has collected them in abun- 
