590 Note on the Genus Spiraculum. [Nov. 
VII.—Note on the Genus Spiraculum. By J. T. Pearson, Curator As. Soc. 
[Presented to the Asiatic Society, and read 30th October, 1833.) 
Class, Mouuusca, Order, TRACHELIPODA. 
Section, Phytiphaga. Family, —————? 
Genus, Spiraculum. 
Animal—unknown. 
Shell—discoidal, upper surface plano-convex, almost flat at the 
top, largely umbilicated; whorls cylindrical; mouth circular ; lip 
thickened, reflected; last whorl a little bent downward toward the 
umbilicus; a shelly, projecting spiracle, or breathing-tube on the 
upper edge of the body whorl, where that whorl touches the preceding 
one. 
Operculum horny ; very thick; formed of several spiral lavers. 
A species of this genus having been found by Mr. Benson, on the 
Rajmahal hills, he formed a new genus for its reception; and de- 
scribed both its generic and specific characters, so far as he knew them, 
in the first number of the Journal of the Asiatic Society. To this new 
genus he gave the name Pterocyclos, and that he was right in ventur- 
ing to institute it can hardly be doubted, when its strongly marked 
characters are considered fully. But the discovery of another species, 
with additional generic characters, has rendered improper a name 
taken from the form of the aperture of a young specimen merely, or 
from a species, as it would appear, far removed from the typical one of 
the genus. Mr. Bunson’s name, therefore, has been altered to that 
of Spiraculum, and the genus, according to characters it is now 
known to possess, differs from all shells that have hitherto come to 
the notice of the naturalist. No land shell besides it, excepting the 
genus Cyclostoma, has a circular aperture ; and it is a curious fact, that, 
in the genus Haliotis only, is there any process at all analogous to 
the shelly tube which form so remarkable a feature in the generic 
character of Spiraculum. 
For the use of this tube analogy must be resorted to in the absence 
of proof; and analogy justifies the supposition of its being intended 
for the purpose of protecting the breathing organs of the animal; 
while it admits of the free passage of air when the mouth of the shell 
is closed by the operculum. Why it should be so; why this genus, 
which seems to be allied closely to the second division of the Colimacés, 
near to Cyclostoma, should have such an apparatus, while Cyclostoma 
has nothing of the kind, though the operculum of the latter shuts up 
the shell as completely as can that of the former, it is not easy to say. 
But it is equally difficult to account for the above-mentioned genus 
