306 Bulletin American Museum of Natural History (Vol. LIII 
The height varies from about 68 per cent to about 76 per cent of the 
length.' A few measurements are intermediate between those of the 
longer and the broader shells, so that we have not thought it practicable 
-to divide the lot into two species; though it is true that a majority of 
the specimens can be assorted into groups of broader and of narrower 
shells. The relative convexity of the valves is also quite variable, the 
diameter running from 54 per cent to 65 per cent of the length in speci-» 
mens measured. 
Fig. 79. a-f, Hupera mediafricana Pilsbry and Bequaert. Stanleyville. Series 
showing variation in contour. The line represents one mm. to the same enlarge- 
ment as the shells. 
Our Stanleyville Hupera agrees in most respects with the descrip- 
tion and figures of E. ferruginea (Krauss). The type of that species was. 
somewhat larger: length, 3.2; height, 2.4; diameter, 1.4 lines; the 
height thus being 75 per cent of the length. Krauss’ figure shows it 70 
per cent. In our shells the height is 68 to 76 per cent of the length. The 
anterior end is not quite so narrow in our shells as in his figures, but the 
latter. were drawn free hand. There is a difference in the rela- 
tive diameter. According to Krauss, the diameter of ferruginea is 44 
per cent of the length. In our shells it runs from 54 to 76 per cent. 
’The length represents the longest axis of the shell, which is somewhat oblique to the hinge-line. 
