70 
ZOOLOGY OF THE FAR EAST. 
discussed by Theodore Barrois ' and by myself % and so far as the MoUusca are con- 
cerned our results are in general agreement. 
The total number of nominal species of Mollusca recorded from the lake is 42 — 
20 Gastropods, belonging to 9 genera, and 22 Lamellibranchiata, belonging to 2 
genera. The Lamellibranchiata are Uitio (s.s.) and Corhicula : the Gastropoda are 
Limnaea, Physa, Melania, Melanopsis, Pyygula, Bithynia, Bithinella, Valvata and 
Neritina (=Theodoxtts). 
The synonomy of the western Asiatic species of Unio is in a most chaotic condi- 
tion and no less than 17 have been recorded from the Lake of Tiberias, but it is very 
probable that half of the names are mere synonyms. This is also the case to a less 
extent with Corhicula, of which 5 have been recorded from the lake. 
No species of Mollusca has been found in the Lake of Tiberias at depths greater 
than about 40 metres. Species of Unio are abundant between 10 and 20 metres, less 
abundant between 20 and 30 metres and scarce at 40. Melania tubercidata has a 
similar bathymetric range, while the Hydrobiid Pyygula harroisi has only been taken 
in a living condition in 25 metres. Only dead shells of the last are found in shallow- 
water. 
vStrictly speaking, therefore, there appears to be no true deep-water MoUuscan 
fauna in the Lake of Tiberias, a fact that may be due to the chemical peculiarities of 
the water. Pyrgida harroisi is the only form not found living at spots shallower than 
20 metres. 
From these brief statements it is clear that no lacustrine MoUuscan fauna of pre- 
cisely the same nature as that of Lake Biwa has as yet been fully discussed from any 
part of Asia ; information about the deep-water Mollusca of the lakes of Celebes and 
Yunnan, where the shallow- water species are fairly well known, would be of the 
greatest possible interest. In Celebes ^ particularly most peculiar forms are known 
among the latter species in lakes that are very deep in places. 
NON-LACUSTRINE FORMS. 
I have already given my reasons for classifying certain species of aquatic Mollusca 
common immediately round Lake Biwa as non-lacustrine and for including Melania 
libertina in this category. It is of course very probable that all or any of these spe- 
cies may stray into the lake in floods or at points where backwaters are formed, but, 
except M. libertina, they do not commonly enter the main body of water. It is im- 
possible that this is also the case with one or more species of thin-shelled Unionidae 
that I have included among the shallow- water lacustrine forms. Anodonta, and pos- 
sibly also Pletholophus , is certainly most abundant at places such as Seta or Komatsu 
where the lake begins to change into a river or is connected with small pools and 
backwaters. In ditches at Hikone only indirectly joined to the lake a species of Ano- 
1 R£v. Biol. Nord France VI, pp. 224-312 (1894). 
2 Journ. As. Soc. Bengal (n.s.), XI, pp. 437-476 (1916). 
3 Sec P. and P. Sarasin's Siisswass.-Moll. Celebes (Wiesbaden : 1898). 
