Mollusca of Lake Biwa. 
47 
Family VALVATIDAE. 
Genus Valvata, Miiller. 
Valvata biwaensis, Preston. 
(PI. Ill, fig. 5.) 
1916. Valvata biwaensis, Preston, op. ciL, p. t6i, pi. ix, figs. 4, 4a. 
V. biwaensis occurs abundantly on a muddy bottom in the deeper part of I^ake 
Biwa. It is not known from any other locality, but does not appear to differ greatly 
from the only other species (except the closely allied V. annandalei) recorded from 
Japan. This species (F. japonica, v. Martens), which has not been figured, was des- 
cribed from a single specimen taken in Hakone lake, a much smaller but deeper body 
of water situated near the Pacific coast of the Main Island of Japan not far from 
Sagami Bay. 
Valvata annandalei, Preston. 
(PI. Ill, fig. 6.) 
1916. Valvata annandalei, Preston, op. cit., p. 162, pi. ix, figs. 5, 5a, 
V. annandalei occurs with V. biwaensis, but not so abundantly. It is perhaps 
no more than a variety of the other ; so far as general form is concerned I have seen 
many intermediate shells, but the differences in sculpture appear to be constant. 
LAMELLIBRANCHIA TA . 
Family UNIONIDAE. 
Genus Hyriopsis, Conrad. 
1900. Hyriopsis., Simpson, Proc. U. S. Nat. Mus. XXII, p. 578. 
The genus is widely distributed in the mainland of south-eastern Asia, from Siam 
to eastern China, and occurs in Borneo. Only one species is found in Japan. 
Hyriopsis schlegeli (v. Martens). 
1879. Unio schlegeli, Kobelt, Abh. Senckenber. nat. Ges. XI, p. 421, pi. xiv. 
1900. Hyriopsis schlegeli. Simpson, op. cit., p. 581. 
This species is fished, chiefly on account of its pearls, at several places on the 
east side of I^ake Biwa in moderately deep water. It is apparently endemic in Japan, 
but I cannot find any particulars of its general distribution. 
Genus Cristaria, Schumacher. 
1900. Cristaria, Simpson, op. cit., p. 583. 
The genus (s.s.) is known from three species, two of which are recorded from 
Japan. Both of these are represented in my collection from Lake Biwa. One of 
them occurs also in the Amur district and in China and Cambodia, while the other is 
endemic in Japan. The third species (C. herculea, Middendorff) is found in eastern 
Siberia, the Amur region and north China. The gefius as a whole has, therefore, a 
more northerly distribution than Hyriopsis. 
