64 ZOOLOGY OF THE FAR EAST. 
the case with the Turbellaria,' the Hirudinea, the Amphipoda, the Isopoda and pos- 
sibly the Oligochaeta. 
On the opposite page particulars are given of my collecting stations in the lake 
at which Mollusca were obtained from depths greater than loo feet. 
Of the seven species dredged at these deep-water stations, three {Vivipara sclateri, 
Melania multigranosa and Corhicula viola) are abundant in shallow water. The two 
Gastropods become graduall}'- scarcer as depths over lOO feet 
Species found in both shallow 111. • n ^ 1 .1 r 
. . are reached , but occur occasionally even at depths oi over 
and deep water. ' ^ 
250 feet. They make their way most readily into deep 
water from the abruptly shelving sandy beaches on the western side of the lake. 
Shells of these species from deep water are not at all dwarfed ; indeed two specimens 
of M .multigrmiosahom 36 fathoms, though much eroded, were the stoutest examples 
taken on my tour. 
Shells of Corhicula viola from between 100 and 200 feet do not differ materially 
from those that live between 10 and 100 feet, though perhaps they never attain quite 
so large a size. Specimens, however, from 260 ft. (Sta. 8) were not only very small but 
also more symmetrical and more inflated than normal shells (pi. Ill, fig. 11). I have 
given my reasons on p. 52 for regarding these shells as dwarfed and not merely young. 
Cristaria plicata is not nearly so abundant a species as V. sclateri, M. multigra- 
nosa and Corhicula viola, but resembles them in being able to live over a wide bathy- 
metric range. Only a few young individuals were taken in deep water (250 feet). 
The true deep-water Mollusca of Lake Biwa are thus reduced to three species, 
Valvata biwaensis, V. annandalei and Pisidium casertanum. No one of these species 
probably occurs at depths less or much less than 100 feet = a little over 30 metres = 
nearly 17 fathoms. From about this point their bathymetric range extends to 320 
feet = 97 metres = a little over 53 fathoms, the greatest depth of the lake. They are 
common at all intermediate depths, but V. annandalei is as a rule less abundant 
than the other two. In their small size, in the thinness of the shells and in the pale 
colour of both shells and soft parts they are characteristic deep-water forms. 
The two species of Valvata are closely related to one another and are apparently 
identical in habits. In the shape ol the shell V. annandalei is not unlike the common 
European V. piscinalis (O. F. Miiller), which according to 
Japanese species of Valvata. atm • i i i- • in •<< < 
ihiele lives in shallow, still or slow-running water on a 
muddy bottom. The closest all}^ of the two Biwa species is probably, however, V. 
{Cinciniia) korotneyi, Lindholm,^' which was found by Korotneff in Lake Baikal on mud 
among weeds in only one fathom of water. This species seems to resemble V. annan- 
dalei in sculpturing and V. hiwaensis in shell-form, but is larger and darker than 
either. Neither species from the Japanese lake is related to those found in deep 
water either in Lake Baikal or in Europe. The only other representative of the genus 
as yet known from Japan was described from a single specimen from Hakone Lake, 
1 See Ijima and Kaburaki, Annoi. Zool. Japon. IX, p. 157 (19 16). 
2 Thiele in Brauer's Susswasserfauna Deulsch. XIX (Mollusca), p. 29. fig. 66 (1909), 
s Korotnefi's Wiss. Ergebn. Zool. Exp. Baikal-See IV (Molhisken), p. 73, pi. i, figs. 63-65 (1909). 
