Dosinia discus (Reeve). 



579 



Measurements. 



Measurements were made indepently on the right and left valves 

 as follows (the lettering refers to Figs. B and C): 



KC-^ 



Fig. B. 



Diagram of left valve in profile. 



C width. A length. B depth. PR palliai sinus depth. 



XY interadductor distance. 



Fig. C. 



Diagram showing mea- 

 surements; interior view 

 of right valve. 



1. Length — the maximum antero-posterior dimension, A. 



2. Depth — B. 



3. Width — the maximum width, C. 



4. Interadductor distance — XY. 



5. Depth of the palliai sinus — PB. 



Length, depth and width were determined by the direct appli- 

 cation of wide-jawed sliding callipers; the internal measurements were 

 taken with spring dividers, the distance being read on the scale of 

 the same callipers. The callipers were provided with a vernier reading 

 to 0;01 cm, and had been calibrated by comparison with a standard 

 scale. It will be noticed that interadductor distance and palliai sinus 

 depth were not measured along the curvature of the shell, but by 

 the shortest distance between the indicated points. The outside 



