a 
338. ZOOLOGICAL RESULTS OF THE PERCY SLADEN 
EXPEDITION TO YUNNAN UNDER THE LEADER- 
SHIP OF PROFESSOR J. W. GREGORY, F.R.S. 
(1922). 
BIVALVE MOLLUSCS. 
By B. Prasuap. D.Sc.. Zoological Survey of India, Calcutta. 
The collection of Bivalves dealt with in this report is 
derived from two sources : (1) the shelis collected by Dr. J. 
Coggin Brown, Superintendent, Geological Survey of India, in 
Yunnan in 1909-1910, and (2) the specimens brought back by 
the Percy Sladen Expedition to Yunnan in 1922. I have also 
had the advantage of consulting the collections made by 
“ Anderson in Yunnan and described by Nevill in 1877 and 
79 
In these collections the bivalves are represented by the 
two families, Unionidae and Cyrenidae Of the former they 
unfortunately contain only a single representative, while the 
latter, the Cyrenidae, is represented by the genera Corbicula and 
Sphacrium. Of the genus Corbicula there are six species in the 
two collections, and this appears to the common freshwater 
bivalve genus in Yunnan. This preponderance of the genus 
Corbicula in Yunnan is what might be expected in view of the 
genus being very well represented in India and Burma on the 
one hand and throughout China, Cambodia and Indo-China on 
theother. The genus is further very well adapted to the changes 
of seasons and the very different types of habitats in ponds, 
lakes and streams. The relationships of the various species are 
discussed in the notes on the various species. but it may be 
noted here, that this genus, owing to the very wide distribution 
of the various species, is not likely to prove of any great value 
‘Or zZoogeographical conclusions. The record of the genus 
Sphacrium from Yunnan is noteworthy 
n conclusion I have to record my deep sense of gratitude 
to Dr. N. Annandale for valuable suggestions and help in 
regard to the localities of the various specimens. 
UNIONIDAE 
No Unionids had been recorded from Yunnan till 1878, when 
Heude | in his interesting work on the fluviatile Molluscs of 
Nankin, China, included the description of a new Unionid from 
187 | Heude, Conch. Fluv. de la Prov. Nanking, IV,. Plate XX XI, Fig. 64 
3). 
