CYCLOSTOMA. 



TESTA tiirbinata, spira plerumque obtusa, an- 

 fractibus rotundatis; apertura fere eirculari, 

 peritremate superne plus minusve angulato, 

 nonnunquam incrassato et reflexo. Operculo 

 spirali. 



This Genus when first established by Lamarck, consisted, 

 like some of the old Linnean genera, of an assemblage of 

 land, freshwater and marine shells, differing among one 

 another most materially in respect to their essential 

 characters. My readers, who have not attended to the 

 progress of knowledge relating to the Mollusca, will be 

 surprized at being informed, that, taking the form of the 

 aperture alone into consideration, Lamarck at first united 

 together in his Genus Cyclostoma, shells, which he after- 

 wards saw the necessity of separating from it, under the 

 names of Scalaria, Delphinula, Paludina, and Valvata; 

 genera, all agreeing very nearly together in the form of 

 the aperture, though differing essentially, not only in the 

 characters and habits of their animal inhabitants, but also 

 in the structure and peculiarities of the shells themselves. 

 Hence we infer the impossibility of attaining anything 

 approaching to a natural ConchoLogicaL System, for if an 

 arrangemant of shells be made from the consideration of 

 their apparent resemblance to each other, it will be found 

 that Ihe consideration of their animals will prove such 

 arrangement of the shells to be far from natural; the 

 affinities of the animals will not at all accord with those 

 of the shells alone. We will, however, endeavour to 

 demonstrate, as nearly as possible, the impropriety of the 

 particular combination above-mentioned, and also to 

 describe the peculiarities of each of the genera that have 

 been thus combined, and to show their relations. 



The present Genus differs from Scalaria, inasmuch as 

 there is never more than one period of growth, conse- 



