172 



PUPILLA, EUROPE. 



elated with about an equal number of P. s. dextroversa of 

 about the same size, we at first were disposed to think them 

 all one race in which the shell was indifferently dextral or 

 sinistral; but on closer study it appears that the dextral 



FIG. 4. Pupilla syngenes avus, Cotypes. Lengths 5.2, 4, 4 and 4.2 mm. 



forms never have the last whorl and aperture abnormal nor 

 are the teeth so deeply immersed, or the parietal lamella so 

 long, while almost every sinistral shell collected in this colony 

 is markedly distorted. It seems, therefore, that although the 

 two forms are of common origin and live together, the dif- 

 ferent direction of the coil probably prevents interbreeding, 

 thus segregating the sinistral stock, which in this colony is 

 now in a late stage of senile degeneration. 



II. SPECIES OF EUROPE AND NORTHERN AFRICA. 



Like the American group, these present all stages in the 

 degeneration of the teeth. Recent European forms have to 



3 teeth, like the American, belonging to the section Pupilla. 

 In Asia the more primitive group Primipupilla, species with 



4 or 5 teeth, lingers on, associated with the modernized 

 forms. 



The variations in teeth, in shape and development of the 

 prelabial crest, have led to the naming of many "varieties", 

 part of them true geographic races, many others being muta- 



