Mollusca of Lake Biwa. 
50 
Zones of life in the lake. 
lake have a summer temperature of over 2()°C. On October ist we found that the 
temperature of mud brought from 260 feet was 8°C., while that of the air was 22°C. 
It is thus manifest that the temperature of Lake Biwa varies greatly, as might 
be expected, with depth as well as with the seasons 
In a general survey of the Mollusca of Lake Biwa based on field knowledge two 
facts stand out prominent — firstly that the species which live among stones and 
rocks are different from those commonly found on a muddy or- sandy bottom, and 
secondly that certain species only occur in deep water. A more careful scrutiny 
reveals a third fact — that a few species, though they can 
hardly be excluded from the lake-fauna, are not really lacus- 
trine but frequent pools, ditches, etc. at the edge of the lake. Except in the 
case of the rupicolous forms, the lines are not drawn exactly ; shallow- water forms 
stray occasionally into deep water and individuals of non-lacustrine species are some- 
times found in the lake. Nevertheless, the facts stated form a convenient basis for 
a biological classification of the fauna. At present this classification can be applied 
to the Mollusca only, but I have the strongest evidence that it will also be found 
applicable to the lake-fauna as a whole, when it has been completely worked out from 
a systematic point of view. 
The lists below are formed by classifying the Mollusca in accordance with this 
scheme, under the headings " Rupicolous," " Shallow- Water," " Deep-Water " and 
" Non-lacustrine." Among Rupicolous species are included those that adhere to 
small stones. 
Rupicolous. 
LiTHOTIS JAI'ONICA. 
Choanomphalus JAPON- 
ICUS. 
Planorbis biwaensis 
Melania libertina 
(dwarfed). 
Melania niponica. 
Melania biwae. 
Bithynia striatula japuni- 
ca. 
Deep-Water. 
Melania multigranosa. 
Vivipara sdaieri. 
Valvata biwaensis. 
Valvata annandalei. 
Cristaria plicata. 
CORBICULA viola 
(dwarfed). 
PiSIDIUM CASERTANUM. 
Non-lacustrine. 
LiMNAEA JAPONICA. 
Melania libertina (typi- 
cal form). 
Vivipara japonica. 
Vivipara malleata. 
Sphaerium heterodon. 
Shallow-Water. 
Melania multigranosa. 
Vivipara sclateri. 
Hyriopsis schlegeli. 
Cristaria plicata. 
Cristaria spatiosa. 
Pletholophus reiniana. 
Anodonta woodiana. 
Anodonta calipygos. 
Lanceolaria bilirata. 
Lanceolaria oxyrhyn- 
CHA. 
NODULARIA JAPANENSIS. 
NODULARIA BIWAE. 
NODULARIA REINIANA. 
NODULARIA HIRASEI. 
? Nodular ia parcedentaia. 
? Pseudodon loomisi. 
Corbicula sandai. 
CORBICULA VIOLA. 
In these fists the names of the species particularly characteristic of the different 
zones are printed in Roman capitals. 
