46 flelix Vatesit. [ ZOE 
these crevices between the shelving ledges, and finding them moist 
and cool, would continue their explorations until they entered the 
chambers of the cave; and thus having easy ingress and egress, they 
have no doubt continued their visits for many years, on the approach 
of the dry season, while some, perhaps, never leave the cave. 
The fact that there are so few specimens found within the cave, 
and so many outside and miles away, zstivating under stones, is 
sufficient evidence that the presence of this mollusk within the cave 
is simply accidental, and that it is not its natural habitat. 
In his remarks upon this shell, Dr. Cooper calls attention to its 
resemblance to Planorbis and Ammonite, its relations to 7. ? poly- 
gyrella and Gastrodonta, and its affinity to Macrocyclis, with all of 
which I agree, and which goes to show very plainly, I think, that 
nature does not represent any particular genus by the shell. If she 
indulges in such freaks as genera at all, she determines that matter 
by modifications of the structure of the animal, and not by the 
object formed or moulded by the animal itself; and this little shell, 
compounded of several so-called genera as it seems to be, is a good 
illustration of this fact. 
In support of this I can do no better than repeat Dr. Cooper's 
own words: ‘‘It would have been supposed to be a Planorbis if 
_ found near water and if the streams in that country had not been 
thoroughly searched by many collectors. It resembles Planorbis 
in the inverted spire and in the partial enclosure of each whorl in 
the next larger, so that the spire shows only a small portion of the 
whole shell. 
_‘*The consequent vertical narrowing of the aperture, and, in- 
deed, of the whole interior, is also found in some species of Plan- 
orbis, but not in any American Helicoid. Indeed, it is inconsistent 
with the character of ‘ Helix,’ as defined by Lamarck, and this 
shell could not, therefore, be embraced in that most comprehensive 
genus. The resemblance to an Ammonite is conspicuous in a lat- 
eral view. It probably belongs to Helicellidze, notwithstanding its 
thickened labrum, which we find also in A ? polygyrella and G. 
interna, and some other species. Though toothless, it is apparently 
nearly allied to the former, in which the spire is flat and of 7 to 8 
whorls. It also shows affinity to Macrocyclis in the oblique flat- 
tening of the outer whorls and its strong deflection near the 
- mouth.” 
