188 EOCENE MOLLUSCA. 
at the end of which is the mouth, surrounded by a funnel-shaped veil: the teeth are 
elongate, subulate, and arranged in two series. The foot is simple, oblong, narrow, 
and truncated in front; im the middle it presents a pore, the function of which is not 
ascertained ; and it bears, on the posterior extremity, a small, ovate, horny operculum, 
barely exceeding in length a third part of the aperture, and very narrow, so as to 
permit the animal to withdraw far within the shell. The epidermis, which covers the 
shell, is thick, and frequently very tenacious. 
The cone-animal is endowed with the power of dissolving the calcareous matter 
on the outer surface of the inner whorls, which are thus made exceedingly thin, 
whatever degree of thickness they may have originally possessed. This power of 
absorption is possessed by many other molluscs, but, according to Mr. George Sowerby, 
is confined to those furnished with an operculum. It affords a valuable assistance to 
the Palzeontologist. 
The present genus, although comprising very many species, remains almost as 
Linneeus left it. The foregoing list of synonyms shows, indeed, that many dismem- 
berments have been proposed; but at present these appear to depend principally 
on differences in the shells. In Klein’s proposed genus MVwéecula, however, the shell 
of which is sub-cylindrical, the animal, according to M. Quoy,* is furnished with a 
large foot, not entirely retractile within the shell; the margin of the muzzle is fringed, 
and the operculum is curved and unguiculate: these peculiarities apparently justify 
the division in question being retained as a sub-genus. 
The wide semicircular notch which, in many of the cones, separates the outer 
lip from the suture, closely resembles the sinus characteristic of the Pleurotome, 
and in some of the fossil species in which the outer lip is generally very much 
curved, it is difficult to determine to which genus the particular shell should be 
referred. In the well-known Eocene species, Conus dormitor (Sol.), for instance, the 
shell outwardly possesses quite as much of the character of a Plewrotoma as of that 
of a Cone; and Mr. Swainson has, in fact, taken it as the type for a genus which he 
has named Conordis, and which, in his circle of affinities of the Conie, he regards as 
the representative of the Pleurotome. ‘This division depends entirely on the external 
characters of the shell: no living representative, I believe, has as yet been found, 
and the animal is therefore unknown. It is certain, however, that it was a true cone- 
animal; for, on breaking the shell of a specimen of Conus dormitor, the inner whorls 
will be found reduced by absorption to a membrane-like thinness ; and the capability 
to effect this is not, I believe, possessed by the animal of P/ewrotoma. The proposed 
genus is not well defined by its author, and is not generally received, although it 
may be usefully adopted as a section of the present genus. The characters appear to 
be the elevated conical spire, the produced base representing the canal which dis- 
* Zoologie of the Voyage of the Astrolabe. 
