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 ; in 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 Palaeontologist. 



The present genus, although comprising very many species, remains almost as 

 Linnaeus 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 Nubecula, 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 Pleurotomae, 

 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 Pleurotoma as of that 

 of a Cone ; and Mr. Swainson has, in fact, taken it as the type for a genus which he 

 has named Conorbis, and which, in his circle of affinities of the Conina, he regards as 

 the representative of the Pleurotoma. 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 Pleurotoma. 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. 



