Mr. Swainson on Achatinella. 83 



and struck out a path which is now followed, almost universally, 

 by British naturalists. To characterize a new form, and to give 

 it a name, is no longer looked upon as a dangerous innovation. 

 Slight modifications of structure may, indeed, sometimes be 

 mistaken for types of a superior group, and placed in a station 

 which they may subsequently be found not entitled to. This, 

 with our present confined knowledge, is inevitable; and if it be 

 a real evil, it is still a very insignificant one, when put in 

 comparison with that, which, from a system of generalizing, 

 leads to the neglect of minute discriminations and rigorous 

 comparison. 



Without a knowledge of the animal inhabiting these shells, 

 it is impossible to say anything on its natural affinities. Yet, 

 so far as we can judge from the shells themselves, they appear 

 intermediate between Lamarck's Bulimus and Achatina : between 

 A.fasciata and achatinella pica, there is, indeed, a much closer 

 resemblance than at first appears ; yet they clearly belong to 

 two distinct geographic groups. 



ACHATINELLA. 



Tetta ovato-contca, spiralis. Columellts basis truncata, incrassata. Labium 



internum nullum, externum interne incrassatum, maryine acuto. 

 Habitat in Oceani Pacijici Insults. 



Shell oblong-conic, spiral. Columellae with the base thickened and truncate. 



Inner lip none, outer lip internally thickened, the margin acute. 

 Inhabits the Islands of the Pacific Ocean. 



(Generic Type. Monodonta semi-nigraLam.) 1 



The shells forming the present group are all of a small size ; 

 the largest not equalling an inch in length. In general ap- 

 pearance they resemble Bulimi, both as regards form, and the 

 proportionate length of the spire, the principal whorl being more 

 or less ventricose ; but in some it is sufficiently short to render 

 the shell trochiform. This circumstance, joined to the thickened 

 and somewhat projecting base of the columella, induces me to 

 believe, that the proposed type of the genus has been mistaken 

 by Lamarck for a marine shell, and described, in his Systeme, 

 under the name of monadonta seminigra. This supposition 

 cannot, however, be verified, unless by a reference to the spe- 

 cimen he described . it is also rendered somewhat doubtful, as 

 he does not quote the figures, in Dixon's Voyage round the 



G2 



