414 MR. G. BUSK ON FOSSIL REMAINS FROM BORNEO. [June 10, 
denticle, whilst the longitudinal exceeds the transverse diameter of 
the crown. 
Fig. 6. 
Dorsum of im. 2, R. sumatranus. 
2. As regards R. etruscus, which, in the crochet and posterior 
vallum, exhibits the same characters as R. sondaicus, the distinction 
from the Sarawak fossils, and from the latter species, is to be sought 
(1) in the dorsal surface, in which the anterior costa is very little pro- 
minent, and much narrower or thinner than in R. sondaicus, and the 
hinder border is not at all raised, so that, instead of a concavity, the 
surface behind the anterior costa presents a convexity. The second 
or median costa also is much wider and more convex, and the third 
