VERTIGO OF JAPAN AND EASTERN ASIA. 157 



added. Length 1.2, diam. 1 mm. Ratio of aperture [to spire] 

 1 :1 (Mouss.). 



Siberia : Vladivostok, Louis Graeser. 



Pupa (Vertigo) denudata MOUSSON, Journ. de Conch, xxxv, 

 1887, p. 19, pi. 1, f. 6. 



' ' Taken at the same point as P. alpestris, but it is not to be 

 confused with that. It is always denuded, with little trans- 

 lucence, whitish, while the other species is corneous and dis- 

 tinctly translucent. P. denudata has % to 1 whorl more than 

 alpestris, its whorls are less close, giving it a longer, slimmer 

 shape; the aperture is more regularly rounded, the outer 

 margin not concave" (Mousson). 



The presence of two teeth on the parietal wall, and of a 

 crest ("perist. . . . extus ruga circumdatum") seem to show 

 affinity with the V. hydrophUa group, but the figure is not 

 sufficiently exact for a critical comparison with the Japanese 

 species. Moreover, the dimensions given are clearly erroneous 



Subgenus PTYCHALAEA Boettger. 



Ptychalaea BOETTGER, Jahrb. Nassau. Ver. Naturkunde, 

 Jahrg. 42, 1889, p. 293. Type by orig. des. V. flexidens 

 (Bas.). 



Similar to Vertigo except that the angular lamella connects 

 by a curved callous ridge with the termination of the outer 

 lip; there is a rounded crest behind the peristome. Type 

 V. flexidens Eeuss. 



Distribution, Lower Miocene to Pliocene of Europe ; recent 

 in the Bonin Islands. 



The type of this subgenus, V. flexidem (pi. 15, fig. 15), has 

 an infraparietal lamella and a suprapalatal denticle. The 

 angular lamella and the rest of the structure agree exactly 

 with the recent species, and I believe that there can be no 

 doubt that the latter belong to Ptychalaea. The Bonin 

 Islands have a highly peculiar snail fauna, doubtless evolved 

 on a far larger land-mass which included all of the present 

 islands. This fauna appears to have been derived from the 

 continent not later than the middle Tertiary, and probably 

 earlier. In Europe the species of Ptychalaea had about the 



