PYKAMIDELLIim 397 



I present an account of many of the animals of Chemnitzia, 

 the most difficult of all the Gasteropodan genera; most of 

 them have been submitted to repeated examinations. The 

 present list is more than fourfold greater than any that has 

 yet been recorded. 



Before I enter on the descriptive matter, it will be proper 

 to say a word or two in explanation of some of the organs 

 of the very singular genus, which, in my method, includes 

 the Odostomia. and Eulimella, and a few of the species of 

 Aclis. 



With respect to the organs of the animal, I will first men- 

 tion the peculiar anterior process styled by most authors the 

 mentum, which I think ought to be considered the muzzle or 

 rostrum, as it is a continuation of the neck, over which a 

 bridge is thrown, formed of the eyes and tentacula ; and close 

 under them, but on 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- 

 nitzia 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 of Natural History/ N.S. vol. vii. 

 p. 464, from a sketch of M. Loven, gives a very good repre- 

 sentation of it; the remaining or terminal portion of the 

 rostrum appears to be mute, and is for more or less of its 

 length attached to the animaPs foot ; in other words, it is less 

 free than the muzzle of the Rissote, 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 Chem- 

 nitzia, which is a long, narrow, thick, distinct, 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, 



