62 
ZOOLOGY OF THE FAR EAST. 
much more abundant than elsewhere ' ; but, speaking generally, the two common 
Gastropod species {Vivipara sclateri and Melania multigranosa) are equally abundant 
whether the bottom be muddy, sandy, or of a mixed nature, whether weeds be pre- 
sent or absent, at all points between lo and lOO feet deep. 
My knowledge of the distribution in the lake of the different species of Unionidae 
is less exact, for it is difficult in some cases to distinguish the different species and 
while in Japan I did not fully understand the specific 
Unionidae of Lake Biwa. . t, • i . 
or even the generic differences. It is, moreover, almost 
impossible to obtain specimens of molluscs that lie buried in mud at the base of a 
luxuriant growth of water-weeds. It will be well, therefore, to give here a statement 
as to the actual depths at which the different genera of Lamellibranchiata were 
dredged by Dr. Kawamura and myself in a living state. 
Depths at which the Genera of LamelIvIbranchiata were dredged in 
Lake Biwa. 
Cristaria 2-3 fathoms ; 41 fathoms. 
Anodonta 1^-7 fathoms ; 2-3 fathoms ; 6-7 fathoms ; 5-17 fathoms. 
Lanceolaria 2-3 fathoms ; 3I fathoms : 5-17 fathoms. 
Nodularia i^-y fathoms ; 2-3 fathoms ; 3|- fathoms ; 6 fathoms ; 5-17 fathoms. 
Corhicula 2-3 fathoms ; 3J fathoms ; 6 fathoms ; 6-7 fathoms ; 5-17 fathoms, 
91^-17 fathoms ; 17 fathoms ; 41 fathoms. 
Pisidium 9i--i7 fathoms ; 31-33 fathoms ; 34 fathoms ; 41 fathoms ; 43 
fathoms ; 53 fathoms. 
In several instances these figures are a little unsatisfactory owing to the sudden 
slope of the bottom near the shore. This makes it impossible, without apparatus I 
did not possess, to fix the exact depth at which a specimen was actually taken into the 
net. It may be stated that all the stations at which depths above and below 100 
feet were recorded in the course of a single haul of the net were close inshore, while 
all those at which the greatest depth recorded exceeded 100 feet vx^ere in the middle 
of the lake. The bottom is always sandy where it descends abruptly. I did not 
take, or at any rate bring away, specimens of Hyriopsis or Pseudodon, but the 
former genus is represented in the late Dr. John Anderson's collection from Lake 
Biwa by a fine series of shells of H. schlegeli. 
If my figures in reference to the six genera of Lamellibranchiata be analysed , it 
becomes quite clear that from a bathymetric point of view Pisidium falls into a 
different category from the others and cannot be dealt with 
Lamellibranchiata of shallow j ^i i i. ^ 
^ater. under the heading Shallow- water Forms," while Cnstana 
must be considered both as a shallow-water and a deep-water 
genus. This is not due to a difference in the habits of different species, for young 
specimens of C. plicata were taken in small numbers from both the depths recorded. 
My figures also provide definite evidence that the bathymetric range of Corbicula 
1 One of the most important fisheries for this species is situated near Seta, the Corbiculae of which enjoy great 
reputation among J apauese epicures. 
