Mollusca of Lake Biwa. 
51 
Nodularia hirasei, Haas. 
191 1. Nodularia hirasei, Haas, op. cit., p. 95, pi. xiifl, figs, i, 2. 
The type specimen of this species, which was only described in 1911, came from 
Yamashiro, a short distance south-west of Lake Biwa. It is by no means uncommon 
in the lake. 
Family CYRKNIDAE. 
Genus Corbicula, Megerle v. Miihlfedt. 
1907. Corbicula, Pilsbry, Annot Zool. Japon. VI, p. 153. 
Corbicula sandai, Reinhardt. 
(PI. Ill, fig. 12.) 
1904. Corbicula sandai, Fischer and Dautzenberg, Miss. Pavie Indo-Chine, H. div.. Ill, p. 442. 
1907. Corbicula sandai, Pilsbry, op. cit., p. 157, pi. vii, figs. 17, 18. 
The name C. sandai is usually applied to the common Corbicula of Lake Biwa, 
which provides a well-known food-product. I believe this, however, to be incorrect, 
for I was able to find very few specimens in the lake in which the ribs were not 
developed on the median portion of the valve — a character that Pilsbry regards as of 
prime importance in distinguishing C. sandai from his C. viola. The only specimens 
in my collection that have this character were taken in the channel east of Oki-no- 
shima at a depth of between 2 and 3 fathoms. They are small, the largest shell 
being 13 mm. long and 13-3 mm. high. Their outer surface is pale olivaceous stained 
with black. The inner surface is whitish stained with pale violet on the hinges and 
with brown on the lower margin. 
The true C. sandai is not known north of Lake Biwa, but has a wide distribu- 
tion in the southern islands of Japan proper. It has also been recorded from Tonkin 
(see Fischer and Dautzenberg). 
Corbicula viola, Pilsbry. 
(PI. Ill, fig. 12.) 
1907. Corbicula viola, Pilsbry, op. cit., p. 158, pi. vii, figs. 7-10. 
I have no doubt that this is the common species of Lake Biwa, but Pilsbry had 
not specimens of the largest size before him in drawing up his description. My 
largest shell is 31 mm. long, 28 mm. high, and 18 mm. thick when the two valves are 
together. Shells of this size are very asymmetrical and have the posterior end much 
produced and distinctly truncate. The nymph and the inner surface of the upper 
cavity often have a peculiar coral-pink colour and the extreme lower margin is tinged 
with brown. Both the exact shape of the shell and the breadth of the nymph vary 
considerably. The external surface is stained with black. Small shells are more 
symmetrical , less brilHantly coloured inside and brighter externally, often bearing 
concentric and alternating pale and dark bands. 
