ODOSTOMIA. Ill 



distinct, although this may depend oil the nature of 

 their food. 



For our knowledge of the animal we are mainly in- 

 debted to Professor Loven, Mr. Clark, and Mr. Alder. 

 An admirable paper by the first of these writers, on the 

 genus Turbonilla of Leach (Kongl. Vet.-Akad. Forh. 

 1846), illustrated by figures of the animal, shell, and 

 operculum, forms the groundwork, and is especially de- 

 serving of careful study. Mr. Clark has supplied us 

 with elaborate details of many species. Although he 

 exalted the science of malacology as the only method of 

 natural classification, he could not help remarking on 

 the singular sameness of his descriptions, and admitted 

 that "indeed it is difficult to divest oneself of the 

 idea that all of them appertain to the same animal " *. 

 Sometimes his power of observation with the microscope 

 must have been more acute than at other times. I can- 

 not otherwise account for his stating that the tentacles 

 of several species which he described are ' ' setose " or 

 " setaceous." This is but partially the case ; and the 

 following account by Mr. Alder of a remarkable pecu- 

 liarity of the structure of the animal will probably 

 explain Mr. Clark's meaning. " 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 revolv- 

 ing wheel, while no cilia are to be found on the other 

 part of the tentacle, except a few rigid, immoveable setse 

 at the apex. In one species, 0. Eulimoides [O.pallida], 

 I have observed the vibratile cilia to extend in a line 

 from the disk down the centre of the tentacle, but con- 

 fined to a very limited space. These ciliated disks are 

 * Ann. & Mag. N. H. Dec. 1850. 



