CHARACTERS OF SOME HYSTRJCOMORPH RODENTS. 427 



Mainly by chamcteivs supplied by the skulls and teeth, Thomas, 

 in the paper quoted fT,bove, showed how the o-enera of Caviinfe 

 might be distinguished. Tlie three of which I know the external 

 characters may be diffei'entiated as follows : — 



a. Ridxeof ear beneath supratragus simple, not valvular ; iiiterramal 

 vibrissw consisting- of two pairs of long- seta9 set on the posterior 

 border of a large nearly naked area behind the cliin ; anus exposed 

 at the summit of a naked or nearly naked area of skin which lies 

 over the testes and shows no trace of glandular depression ; penis 

 projecting from lower end of this area" Galea. 



a'. Above-mentioned ridge valvular ; interramal vibrissa; absent or at 

 all events typically indistinguishable; anus concealed in the sub- 

 jacent glandular area. 



h. Claws 'elongated ; digital pads flat or lightly convex ; a sin^-ie 



'^"'•P^lP'"^ ^■■■■- ":.. Cavia. 



h'. L'hiws quite short ; digital pads compressed ; carpal pad double... Kerodon. 



