322 Mr. W. Clark on the Animal o/Dentalium Tarentinum. 



between the animals of the two genera. I believe, with the ex- 

 ception of M. Deshayes's monograph, nothing has been done to 

 elucidate this curious molluscum ; and as I think that eminent 

 malacologist has mistaken the uses of some of its organs, I am 

 induced, by the facility of obtaining live specimens of the Den- 

 talium Tarentinum, to review and augment what is at present 

 known of it : the present species inhabits the coralline zones of 

 the South Devon coasts, five or six miles from land, in twelve or 

 fifteen fathoms water. 



Dentalium striatum, Montagu. 

 Tarentinum, Lamarck. 



Animal yellowish white, conically elongated, mantle circular, 

 anteriorly thick and fleshy, edge dentated, posteriorly of the 

 thinnest texture ; the penultimate and antepenultimate portions 

 of its margin are bounded by two intense white muscular elastic 

 cordons ; the united action of these has the power of completely 

 opening and closing the anterior aperture; when at rest, the 

 animal, including the foot, is entirely inclosed by the tougher 

 part of the mantle which supplies the place of an operculum. 



The foot is a very long and singular organ, placed in the cen- 

 tre of the anterior end of the body, and from its position is ap- 

 plicable for use in every direction ; it is divided into three parts : 

 the anterior one is a pointed cone acting in some measure as a 

 tentaculum, and lies in the middle portion, which consists of two 

 lateral, sinuated, symmetrical flaps or tenacula, that are usually 

 protruded simultaneously with the terminal portion, and are the 

 parts subservient to the animal's very confined locomotion, to 

 turn from side to side by using the lateral appendages as points 

 d'appui, and also to climb and secure its food from the stems 

 of the foraminiferous polyparia ; the third or basal section is a 

 long flattish pedicle deeply grooved on its upper and lower sur- 

 faces, extending to the base of the stomach, into which it opens, 

 as it is hollowed out as far as the tenacular flaps, but there is no 

 passage to the exterior surface. I have failed to discover the 

 reason for this connection with the stomach : the hollow part is 

 filled with water, but from what source does not appear, though 

 I think it must come from the buccal aperture ; the use of this 

 singular structure is clearly to augment the flexibility of the 

 foot, as the animal frequently and suddenly doubles it up as the 

 elephant does its trunk ; and also to withdraw the two anterior 

 parts into the hollow portion : this retractile action is necessary 

 in consequence of the peculiar mouth of the animal and rigid 

 character of the anterior end of the mantle, to convey the sus- 

 tentation captured by the tenacula into the cavity of the mantle 

 within the reach of the very short foliaceous cirrhi at the buccal 



