NOTES ON THE PALUDINA-SPECIES OF JAPAN. 89 



Pal. oxytropis var. Sciatevi (fig. 14) ( = Pal. Sciatevi v. Fr.) is dis- 

 tinguished from the typical form hy having oval, thicker and heavier 

 shell, with an obtuse apex ; whorls swollen, but not so much as in the 

 above variety, and separated by very shallow sutures. Raised lines 

 persist in each whorl, though not so prominent as to give rise to angles 

 at the peristomal margin. Aperture oval, with obtuse angles above and 

 below ; edge of peristome very thick, and the outer lip slightly expanded 

 outwards. 



Notwithstanding the differences of adults, the young of the typical 

 form and of its varieties all agree in characters. The embryo-shell 

 (fig. 8) is light green and consists of five whorls, with a conical pointed 

 spire. Three raised lines are distinctly to be seen. The last of these 

 lines brings about a conspicuous angle at the margin of the outer lip, 

 the aperture showing four angles in all. The general shape of the shell 

 is that of a double cone. 



The main features of embryonal characters above referred to are 

 retained during the growth of the shell (figs. 8—11), to be directly con- 

 tinued further on into the adult stage in the case of typical oxytropis, 

 but to deviate at a certain period of growth into the respective definitive 

 characters of japonica and Sciatevi, where these are concerned. This is 

 the ground on which I base my conclusion that oxytropis represents the 

 primitive stock, whence japonica and Sciatevi have differentiated. 



I will here let follow an account of the specimens collected by myself 

 at different localities in the north-eastern provinces to illustrate how 

 this species varies. 



1) Most of the specimëns from a muddy stream in Yamagata village 

 near Lake Inawashiro, Prov. Iwashiro, distinctly show the characters 

 of typical oxytropis. Fig. 12 was drawn from one of the specimens 

 collected at that place. In four out of fourteen specimens obtained, the 

 spiral raised lines were either indistinct or nearly absent while the 

 whorls were more or less swollen, which characters made them approach 

 either japonica or Sciatevi. In the majority of specimens the three 



