Mr. J. G. Jeffreys on Chemuitzia and othei- Mollusca, 465 



petent scientific observer like Professor Loven has seen, de- 

 scribed, and figured, must have a real existence; and conse- 

 quently that Jeffreijsiu, vi^hich is acknowledged to have a simple 

 longitudinally cleft mouth, like the Rissoce, cannot by any 

 stretch of imagination be brought into the same genus. The 

 one belongs to the family of the Pi/ramidellidce, the other to the 

 Littorinidce, where the authors of ' British Mollusca' have cor- 

 rectly placed them. Having in my former letter taken a review 

 of the differences that exist in nearly all the organs of the two 

 genera, it is unnecessary here to recapitulate them : it may be 

 permitted me, however, to mention one peculiar character in 

 Chemnitzia (or Odostomia), also distinguishing it from Jeffreysia, 

 which does not appear to have been noticed by British authors, 

 though it has not escaped the observation of M. Loven. It is 

 this : — that there exists near the apex of each ear-shaped tentacle, 

 just within the inner margin, a circular area or lobe, set with 

 strong vibratile cilia, which are in constant motion during the 

 life of the animal, giving that part the appearance of a revolving 

 wheel, while no ciha are to be found on the other parts of the 

 tentacle, except a few rigid, immoveable setse at the apex. In one 

 species, O. Eulimoides, I have observed the vibratile cilia to ex- 

 tend in a line from the disc down the centre of the tentacle, but 

 confined to a very limited space. These ciliated discs are very 

 cui'ious, and no doubt indicate the seat of a particular function ; 

 probably they are a modification of the organs of smelling. 

 They have not been observed in other genera. 



I shall now take my leave of this subject, confidently antici- 

 pating that future investigations will confirm the correctness of 

 my remarks. 



I remain, dear Sir, 



Yours very truly, 



Joshua Aldek. 



XL VI. — On Chemnitzia and other Mollusca, in answer to 

 Mr. Clark. By J. Gwyn Jeffreys. 



[^Vith a Plate.] 

 To the Editors of the Annals of Natural History, 

 Gentlemen, Norton, near Swansea, May 15, 1851. 



My attention has been called to the recent letters of Mr. Clark 

 in your Magazine on the British Chemnitzia, and as I have be- 

 stowed some attention on this group of Mollusca, I trust I may 

 be excused in making a iew remarks. But previously to doing 

 this, I can assure my esteemed friend, the v\Titer of those letters, 

 Ann.&fMaff.N.Hisi.8er.2. Vol.yu. 30 



