Japanese Species of the Genus Corhicula. 
525 
remotis regularibus obtecta " and further elaborates in the German description " Die 
Oberflache der sehr dicken Schale ist mit regehnassigen, weit (iiber 1 mm.) von einander 
abstehenden, concentrischen, ziemlich stark hervortretenden Rippen bedeckt, (ca. 18), 
die in der Nahe des Hinterrands sich ziemlich plotzlich wie geknickt nach oben bie- 
geri." This character of the ribbing is quite constant in the large series examined b}^ 
me, except that in some of the medium-sized shells the ribs become fainter just before 
bending upwards near the posterior margin ; the shells in such examples appear as 
being nearly smooth in this region, but in no case have I found a specimen with the 
median portion of the valves smooth. 
C. sandai is a very variable species. The young shells are nearly symmetrical, 
but become more and more asymmetrical with age. Young and medium-sized shells 
correspond in outline to the figures of Reinhardt, Pilsbry's figures 7 and 8, and 
Annandale's 10&, 11 and 12, older shells are like Pilsbry's figures 9, 10, 17 and 18, and 
the fully-grown shells resemble the one figured by Annandale as loa. The largest 
shells which I have seen are still more asymmetrical. They are more elongate with a 
narrow, wing-like, drawn-out posterior margin, which is distinctly truncate. The 
sculpture on this region is of the type described by Pilsbry for his new species 
C. viola. 
The colour of the shells is also very variable. Mostly the young shells are lemon- 
yellow in colour, but with age this is replaced by brown with only traces of yellow, 
while full-grown specimens are black. The nacre below the pallial line is shinning 
violet, and dull whitish grey above it, but in some shells it is of a light salmon colour 
with only streaks of violet shining through. The shells also vary to some extent in 
thickness. 
Reinhardt's largest specimen was 24 ram. in length, that of Pilsbry's was 27 mm., 
while those collected by Dr. Annandale were as much as 31mm. long. The largest 
specimen before me from the Hamburg Museum, presented to the institution by Herr 
Lenz from collections made by him in 1896 near Sita, Omi, L^ake Biwa, is 34 mm. 
long. 
The type-series was obtained from near Kyoto, while the very large series 
examined by me were all collected at different places and times in Lake Biwa in the 
same district. 
Relationships : — C, sandai is allied to C. japonica Prime, but is distinguished by 
the less shining periostracum, the different sculpture and the shape of the shells. 
Kobelt iop. cit., p. 438) considered it to be allied to the Chinese C. cyreniformis 
Prime. 
Fischer and Dautzenberg's ' record of C. sandai from Indo-China does not appear 
to be correct as the species is true Japanese, being confined to the southern part of 
Japan proper, and not occurring north of Lake Biwa. 
1 Fischer and Dautzenberg, Mission Pavie Indo-Chine III, p. 442 (1904). 
