CHAP. VI. SUB-GENERA OF CLAUSILIA. 183 



rare and remarkable shells are all from Brazil ; and they 

 establish, in the clearest manner, the passage between the 

 European ClausilicB and the South American Auricula. 

 We have now arrived at that particular sub- genus which 

 is to connect the present group with the genuine Pupa. 

 This union is effected by those small European shells, 

 hitherto placed in the latter genus, which we have sepa- 

 rated under the name of Pupella. This sub-genus, in 

 fact, may be looked upon as the common point of union 

 where the sub-families Bulimina and Achatina are 

 united. They are at once distinguished by having both 

 sides of the aperture toothed ; and not, as in Pupa, the 

 inner lip only. Some uncertainty hangs over what shells 

 are the true types intervening between Pupella and Balia. 

 The passage, indeed, is very easy, if we suppose it to be 

 made by certain little shells of Europe (as the P. mus- 

 corum, fragilis, dolium, and umbilicata of Drap.) which 

 have no teeth on the outer lip, but sometimes one on 

 the inner j while the shortness of their spires would 

 distinguish them from Balia : or this, perhaps, is the 

 place where some of the smaller shells, analogous to our 

 Gonospira, should be placed ; at all events, we have in 

 Pupella such a close approximation to Balia, that the 

 circle of the genus Clausilia may be considered almost 

 perfect : at all events, we cannot consider either Ala or 

 Vertego as sub-generic types, merely because they differ 

 from our Pupella by the position of their aperture ; while 

 Azeca of Leach, as a sub-genus, is equally questionable. 

 We presume, therefore, that the types here mentioned 

 form the circle of Clausilia. We have already com- 

 pared them with those of the Pupa, in conjunction 

 with the genera of the HELICIN^B, we shall now, how- 

 ever, bring the sub-genera of Pupa and Clausilia more 

 immediately and exclusively together ; when it will be 

 more readily perceived that the hiatus between Balia 

 and Pupella might be filled up by some of the shells 

 just mentioned. 



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