196 Mr. W. Clark on some of the Animals of the Chemnitziae. 



the upper part of the base, or hinder portion of the rostrum, is 

 the proboscidal orifice, from which, though a circumstance of the 

 rarest occurrence, I have in three species seen the evolution of 

 that organ, in the Chem. pallida, C. acuta and C. plicata ; the 

 animals kept it exserted from half a minute to three minutes. 

 Mr. Alder's figure in the 'Annals,' N. S. vol. vii. p. 464, from a 

 sketch of M. Loven, gives a very good representation of it ; the 

 remaining or terminal portion of the rostrum appears to be 

 mute, and is more or less of its length attached to the animal's 

 foot; in other words, it is less free than the muzzle of the 

 RissocBj of which I consider it the representative and remnant, 

 and which it will be seen has entirely vanished in Eulima. 

 Though authors speak of a mentum in that genus, I can find 

 none ; they have, I think, mistaken for it the upper margin or 

 flap of the foot, which in front is divided by a narrow groove : 

 this separation is more or less apparent in most, if not in all, 

 spiral Gasteropoda; it has however little resemblance to the 

 rostrum of the Chemnitzice, which is a long, narrow, thick, di- 

 stinct, and otherwise variable organ, proceeding from the neck 

 as its continuation, and has much the aspect of a mute rissoidean 

 muzzle ; whilst the margins of the foot of the Eulima and other 

 Gasteropoda, and they are generally present in the Chemnitzice, 

 are to assist flexibility on the march, in the same manner as the 

 digitations of the feet of all animals assist progression. Loven, 

 who has described the mentum in his genus Turbonilla, our 

 Chemnitzia, has not, though he has described the animal of 

 Eulima, mentioned the presence of a mentum or rostrum in that 

 genus. 



The point of issue of the proboscis, from the upper part of the 

 rostrum, is more advanced and visible in Chem. plicata than in 

 any other species I have yet examined ; it was from this animal 

 that it continued evolved more than three minutes, afi'ording me 

 a sight that falls to the lot of few malacologists. I believe I 

 speak within compass, when I state that I have examined more 

 than a thousand live Chemnitzice of twenty species, yet, except on 

 the three occasions alluded to, I never witnessed its exsertion. 



All the ChemnitzicB have a semitubular fold more or less deve- 

 loped in the mantle, which, though it issues at the upper angle 

 of the aperture, close to the debouchure of the rejectamental 

 orifice, appears more like a branchial one than for faecal func- 

 tions. In the true C. acuta it is largely exserted and very con- 

 spicuous. Can this fold be analogous to the process I have de- 

 scribed at the same point in many of the Rissoce ? Can it have 

 the double, though apparently incompatible, duties of depura- 

 tion, and to supply the animal, when the operculum on certain 

 exigencies is required to be nearly closed, with the branchial 



