280 
GAMMA RIDiE. 
seen than in the present genus as compared with Leu - 
cothoe and Stimpsonia. In these genera the first pair 
forms a most effective organ of prehension, the pre- 
hensile power being, however, developed in different 
joints of the limb. In Leucothoe and Stimpsonia it is the 
carpus which is remarkably produced, but in Aora the 
metacarpus becomes the analogue of the carpus of the 
two former genera. 
At first sight it might seem that this genus should be 
incorporated in that of Microdeutopus, but the fact of 
exotic species possessing the characters here laid down 
sufficiently warrants their retention as a separate genus. 
We think it not improbable that further observation 
may induce the removal of the closely-associated genera 
in which the peculiar tubular kind of tail-scale is found, 
from the position in which we have placed them among 
the Gammarides , to one nearer the genus Ncenia among the 
Podocerides. The difference in the relative strength of 
the two pairs of antennae will also afford some clue to 
the propriety of such a change of position. 
