iy ee ee ee ee 


1923.] Zoological Results of Expedition to Yunnan. 427 
in the district of Tsing- Yang, while the specimens now assigned 
to it were collected by the Percy Sladen Expedition in Chitien 
Valley in the Bheti stream, a tributary of the Yangtse-Kiang 
River. 
Measurements :—(in millimetres). 
1 2 3 + 
Length wig 15°8 10°8 10 8:9 
Height i 13°6 10°3 8°2 eat 
Diameter re 92 se | 5-1 4°3 
Corbicula praeterita Heude. 
(Plate 16, Figs. 13, a-d). 
1885. Corbicula praeterita, Heude, op. cit., Plate VII. Fig. 40. 
This interesting lacustrine species was described by Heude 
from the Lake Po Yang, and I assign a large series of specimens 
collected from the banks of the Lake Tali (Erh hai) by Dr. J. 
Coggin Brown of the Geological Survey of India, in 1909-1910, 
and by the Perey Sladen Expedition from the northern banks 
of the same lake in 1922. 
The shells of this species are of a medium size, thick- 
shelled ; with prominent, swollen and somewhat posteriorly re- 
curved umbones. The sculpture on the greater part of the 
valves is usually eroded, but in shells where it is preserved, it 
consists of regular, concentric, strongridges. The hinge is very 
strong and broad, with the muscle-scars greatly abutting on the 
lateral teeth. The lateral teeth together with the median teeth 
orm a deep arch which, however, is greatly indented on the 
two sides of the median teeth, marking them from the laterals. 
The nymphal area is large and smooth. Most of the shells 
before me are subfossil, and it is not possible, therefore, to be 
certain about the colour of the fresh shells, but the more recent 
ones are of a dark-brownish to black colour, and the nacre 
shows traces of an olivaceous tint. 
seasons of growth followed by sudden and long periods of sus- 
pended activity. This seems to be connected with the peculiar 
