56 
ZOOLOGY OF THE FAR EAvST. 
It is thus clear that there is a distinct endemic element among the Mollusca of 
Lake Biwa. The apparent strangeness given to this element by the occurrence of 
two such unexpected genera as Lithotis and Choanomphaliis is probably more appar- 
ent than real, but it is worthy of notice, in reference to the former, that another 
peculiar genus hitherto regarded as exclusively Indian {Camptoceras ') has also been 
found quite recently in Japan. If the anatomy of the Indian and Japanese forms 
should prove to be similar, the probability is, in both cases, that other species will 
be found sooner or later in many other parts of eastern Asia. 
The true Japanese molluscs found in Lake Biwa and its immediate vicinity are 
not in themselves by any means remarkable, but the distribution in Japan of the 
different forms is interesting in that it is by no means identical. Unfortunately the 
range of the Japanese fresh-water Mollusca has as yet been studied in most cases but 
incompletely. Nodidaria hirasei, as has already been noted, is known only from the 
central part of the Main Island ; Limnaea japonica occurs on the islands of Hokkaido 
and Shikoku, while Melania libertina and Vivipara malleata are distributed over the 
greater part of the Japanese Empire, in the one case from Hokkaido, and in the other 
from the north of the Main Island, to Formosa. 
It is worth while to consider the distribution of the seven species found on the 
mainland of Asia in some detail, species by species. 
The distribution of Limnaea pervia is incompletely known. It was described 
from China and has been recorded from Tokyo on the Pacific coast of the Main 
Island of Japan 
Biihynia striatula appears to be mainly a southern species. It has been recorded 
from Cambodia and from several locahties in central China. The Japanese race 
(var, japonica, Pilsbry) varies considerably in the very character that distinguishes 
it from the forma typica, viz., in the development of the spiral ridges ; it is only 
known from the Main Island. 
Cristaria plicata is a very variable species, evidently sensitive to differences of 
environment ; it has been found in many localities on the mainland of north-eastern 
Asia including some as far north as the Amur, and also in Cambodia.' 
Anodonta woodiana has on the whole a somewhat more southerly distribution, 
though it has been reported doubtfully from the Amur region ; in a south-westerly 
direction its range extends as far as Siam. 
Lanceolaria hilirata seems to be a scarce form. It is only known from Cochin- 
China and Japan and is closely related to the endemic Japanese L. oxyrhyncha. It 
must be regarded as an essentially southern form, but its precise distribution in 
Japan is unknown and it has probably been confused with L. oxyrhyncha. 
Corbiciila sandai has a somewhat similar range, but there is definite evidence 
that it does not occur north of Lake Biwa, in which it is not at all common. 
i Preston, Ann. Mag. Nat. Hist. (8) XVII, p. i6o (1916). My specimens, which apparently belong to an undescnbed 
species, were obtained for me through the kind offices of Mr. Hirase by Mr. S. Tetsuaki Kira, who informed me that the 
species was by no means uncommon at Kogamura in the Osaka district. I kept them alive for some weeks ; they were 
entirely aquatic in habits, remaining among water-weeds in an aquarium. 
^ Preston, Rec. Ind. Mus. VII, p. 280 (1912) 
