302 
ZOOLOGY OF THK FAR EAST. 
Bithynia longicornis, Benson. 
Hypsobia minuscula, sp. nov. 
Stenothyra decapitata, sp. nov. 
Pseudovivipara hypocrites, gen. 
et sp. nov. 
Family Assimineidae. 
Assiminea scalaris, Heude. 
Family Viviparidae. 
Vivipara lapillorum (Heude). 
Vivipara catayensis (Heude). 
Family Cyrenidae. 
Corhicula sandai, Rein. 
Sphaerium, sp. 
IvAMELLIBRANCHIATA . 
Family Mytilidae. 
Modiola lacustris, von Martens. 
Family Unionidae. 
Anodonta woodiana (Lea). 
Nodularia dactylina (Heude). 
Nodularia douglasiae (Griff). 
It is not possible, except to a very limited extent, to distribute these molluscs 
into zones of life as was done with the molluscs of Lake Biwa, mainly because 
conditions are much more uniform throughout the lake. One species [Assiminea 
scalaris) is quasi-aquatic rather than aquatic, while four {Vivipara lapillorum, Bithynia 
striatula, Bithynia longicornis and Modiola lacustris) are found chiefly near the 
margin among small stones or on the roots of trees. The two species of Bithynia 
and the Vivipara are also found in canals in the neighbourhood. Only three species 
appear to be definitely lacustrine, occurring in large numbers on the bed of the lake. 
They are Stenothyra decapitata, Hypsobia minuscula and Corbicula sandai. The other 
species were found chiefly in narrow creeks and channels and all of them probably 
occur also in canals and waterways. 
Considered as a whole the Molluscan fauna of the lake possesses two outstanding 
peculiarities: — ^(i) the small size of its members and (2) the estuarine element in its 
composition. 
Some of the gastropods, if they are not actually peculiar to the Tai-Hu, are 
probably small wherever they occur, for example the Stenothyra, the Hypsobia and 
Assiminea scalaris, which has also been found in other localities in the same district. 
At least five species {Bithynia longicornis, V ivipara lapillorum, Modiola lacustris, 
Anodonta woodiana and Corbicula sandai) are smaller in the lake than they are in 
more favourable localities. There is, moreover, a scarcity in the lake-fauna of 
the large Viviparidae of the Vivipara chinensis group, which are characteristic of 
the aquatic fauna of the Yangtse valley as a whole, but perhaps mainly paludine. 
Still more characteristic of the latter fauna are the gigantic Unionidae {e.g. Cristaria 
herculea) not uncommon in some parts of the Yangtse delta. No trace of any such 
species was found in the lake. It is clear, therefore, that in the Tai-Hu conditions do 
not favour the attainment of large size among the molluscs, though this character is a 
feature of the more extended fauna of which that of the lake forms a small section. 
Our knowledge of the conditions of life in different parts of the Yangtse system 
is still rudimentary, but among the unfavourable factors present in the Tai-Hu it is 
probable that we must reckon the muddiness of the water, its shallowness (which 
prevents the fauna from seeking shelter from extremes of temperature in the depths) 
