Mollusca of Lake Biwa. 
69 
that the true deep-water forms are of northern origin , but that even warm-water 
genera such as Corhicula and Melinia can occasionally survive at considerable 
depths. 
Very few molluscs have been described from depths as great as or greater than 
20 metres in Asiatic lakes, but particulars are available in at least two instances in 
the Palaearctic part of that continent. These are lyake Baikal in northern Siberia 
and the Lake of Tiberias in Palestine. Practically no information has been published 
about the deep-water shells of the lakes of the Oriental Region. 
The vast area of Lake Baikal, the cold climate in which it is situated and other 
geographical factors produce conditions very different to those found in a comparatively 
small and relatively warm lake such as Lake Biwa, but it is interesting to compare the 
faunas, because both belong, generally speaking, to the eastern part of the Palaearctic 
Region, Lindholm's monograph of the Mollusca of Lake Baikal provides abundant 
material for comparison. In his list of species he includes the 
Deep-water fauna of Lake 
names of 89, of which 53 (59"5 /^) have been recorded from 30 
metres or over, but of these only 5 (about 5 '6°/^) appear to be 
true deep-water forms, occurring only in water over 100 feet deep. In Lake Biwa the 
corresponding percentages are 2i'2% and 9%^ non-lacustrine species being included 
in both cases. The warm-water genera Corhicula and Melania are not found in the 
Siberian lake, in which three endemic genera {Baikalia, Benedictia and Kobeltococklea) 
occur. 
The Baikal deep-water species are : — 
Choanomphalus westerlundianus (36 m.) 
Baikalia flori (96 m.) 
B. subcylindrica (53 m.) 
B. tenuicosta (53 m.) 
B. wrzesniowskii (50-53 m.) 
Thus, only one species belongs to a genus represented in the Biwa fauna. More- 
over, the only species of this genus known in the Japanese lake is found in shallow 
water close to the margin. It is noteworthy, however, that it attaches itself to small 
stones, which in Lake Biwa are only present near the shore, and that the deep-water 
Siberian form was also found among stones. 
The lake of Tiberias, which lies in latitudes approximately the same as those in 
which Lake Biwa is situated, but on the other side of Asia, 
Mollusca of the Lake of . . , . ,i i i --i. ^.t, t „ „ 
j.j,^^.^^ IS m some respects more strictly comparable witii the J apan- 
ese lake than Lake Baikal. It is a comparatively warm lake 
and lies in hilly country, but whereas Lake Biwa is a httle over 300 feet above sea- 
level, the Lake of Tiberias is more than 600 feet below sea-level. A more important 
difference lies in the fact that the water of the Lake of Tiberias is distinctly brackish 
and has a peculiar effect on Molluscan shells that apparently renders it impossible for 
thin-shelled species to .survive. Moreover, the Lake of Tiberias is only about 14 miles 
long and probably at no point more than about 50 metres deep. Its fauna has been 
