90 CLASS III. GASTEROPODA. ORDER VI. PULMOBRANCHIATA. 
Family 3. CYCLOSTOMACEA. 
Testa aut globosa, aut turrita, apertura rotunda, vel semilunari, labro 
plerumque reflexo, canali aut fissura prope ad marginem interdum 
inciso. Operculum vel corneum, vel calcareum. 
We propose to establish this family for the purpose of associating toge- 
ther in one group the operculated pulmoniferous Gasteropoda, the greater 
part of which are terrestrial. Lamarck included all those that were 
known to him with the Colimacea, but the necessity for distinguishing 
them is obviously founded upon the important difference of their being 
furnished with an operculum. Gray has subdivided this portion of the 
class into no less than three families, Truncatellide, Cyclostomide, and 
Helicinide ; and the first of these is entirely removed from the others, 
upon the supposition that they are pectinibranchial water-breathing mol- 
lusks, incapable of existing in air: we do not however think that such is 
the case, nor do we see that our position is at all negatived by the expe- 
riments of Mr. Lowe. De Blainville, again, for reasons unknown to us, 
has widely separated the Cyclostomata from the Helicine, although the 
only author who ventures to dispute their close affinity: the first of these 
genera is referred to his family of the Cricostomata, between the Valvate 
and the Paludine ; the latter to that of the Ellipsostomata, after the Am- 
pullarie, which, as strangely, follow the Phasianelle. 
The shell of the Cyclostomacea varies exceedingly in form, being either 
globose or turrited ; the aperture is round or semilunar, and the lip, which 
is generally reflected, is sometimes indented near the columella with a canal 
or fissure. The operculum, which is common to all, is either horny or 
subcalcareous. 
We divide this family into four genera : 
Pupina. CycLOSTOMA. 
TRUNCATELLA. HE icina. 
