PYRAMIDELLID#. 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, im my method, includes 
the Odostomie and Eulimelle, 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 animal’s foot ; in other words, it is less 
free than the muzzle of the Rissoe, 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- 
nitzie, 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 Eulime and other Gasteropoda, 
