DISTRIBUTION OF PUPILLIDAE. 163 



Both genera and species are most numerous in the North 

 Temperate Zone; going south the northern genera gradually 

 drop out, until in Argentina only Gastrocopta remains ; how- 

 ever, the South American Pupillidae are quite imperfectly 

 known. In the tropics several genera are added, Bothriopupa, 

 Pupisoma and Sterkia, the last two barely entering the lower 

 border of the Nearctic Realm. The Cocos Island species re- 

 ferred to Nesopupa seems to be a stray from Polynesia, but it 

 needs anatomic comparison with Bothriopupa. 



The distribution shown in the table above apparently indi- 

 cates successive invasions from Asia, which spread southward 

 to distances determined by the date of introduction and the 

 adaptability of the stocks. The gastrocopts and early verti- 

 gines apparently came in not later than Oligocene. The 

 genera which presumably came later, such as Pupilla s. str., 

 Vertigo s. str., Columella and Zoogenetes, differ but little 

 from the old world forms or are specifically identical, and 

 have made the least progress southward. 



The only endemic American genera are GihhuUna, ChaenaxiSy 

 Sterkia and Bothriopupa. Endemic subgenera of Gastrocopta 

 are: Immersidens, Vertigopsis, Privatula and Geminidens. 

 Pupilla has the endemic subgenus Striopupilla ; Pupoides the 

 subgenus Ischnopupoides, and Vertigo the subgenera Vertil- 

 lopsis and Angustula. Of the endemic genera, Chaenaxis and 

 probably Gihhulina are derivatives of the Gastrocopta s. str. 

 stock. I suspect that Immerside^is came from the same stock, 

 but pending anatomic evidence or other significant data, 

 its place in the series remains uncertain. The folicolous 

 Bothriopupa has the appearance of an Americanized Neso- 

 pupa, and from Dr. H. B. Baker's observations, agrees with 

 that group anatomically. The terrestrial Sterkia may be 

 presumed to be derived from some ancestral N esopupa-\\kQ 

 group which reached America from Asia, probably in Paleo- 

 cene times. 



Gastrocopta s. str., Pupoides and Pupisoma are common to 

 the tropics of both hemispheres. Pupoides appeared in a 

 practically typical species (vol. 27, p. 248) in the Upper 

 Oligocene (Tampa silex bed) of Florida (at that time insular. 



