IQIo.| A. ALcocK: Classification of the Potamonide. 259 
lobe is falciform and lies behind the incisor process of the man- 
dible ; the ventral iobe, which is a broad oval plate, more or less 
covers the exposed stirface of the incisor process. Very commonly 
the abdomen of the adult male is broad at base and is suddenly 
narrowed at the 5th or 6th segment; but, whether this is so or 
not, the length of the 6th segment is hardly ever less than (often 
exceeds) its minimum breadth, and the 7th segment is elongate- 
triangular or tongue-shaped—not broadly triangular. 
The subfamily is restricted to the Old World, and is repre- 
sented in Asia, Africa, the Malay Archipelago and Australia. All 
the Potamonide found in peninsular India belong to this sub- 
family. 
It has already been mentioned that in certain Potamonine the 
terminal joint of the mandibular palp, when casually examined, 
appears to be bilobed: in any case of doubt the palp should be 
removed and denuded, or, better still, allowed to dry. 
The following table shows the diagnostic characters of the 
constituent genera. The geographical distribution of the several 
genera cannot be stated with precision, since in the descriptions 
of species the points most necessary for focus are often not 
recorded :— 
SYNOPSIS OF THE GENERA AND SUBGENERA OF 
GECARCINUCINAS. 
Front in adult either not wider 
| than or less than half again as 
wide as the orbit - ete KA 
4 Front in adult usually much wider 
| than, but never less than one- 
and-two-thirds as wide as the 
orbit Ey ae yea 
Lower outer corner of orbit pro- 
5 duced into a sort of gutter .. GECARCINUCUS  (Penin- 
sular India). 
Orbits normal .. ss .. CYLINDROTELPHUSA 
(Peninsular India, New 
Guinea). 
= 
Upper border of merus of chelipeds 
\ with a subterminal spine! Beet 
Z | Upper border of merus of chelipeds 
. without any subterminal spine.. 
Post-orbital crests prominent .. Subgenus PARATELPHUSA 
(Asia, Malay Archi- 
pelago, Africa). 
Post-orbital crests faint or obsolete PERITELPHUSA (Malay 
Archipelago). 
. 
| Except in Paratelphusa blanfordi, a Baluchistan species with broad spooned 
fingers, and in a few other species which, however, can be distinguished by having 
the antero-lateral borders of the carapace strongly spinose. 
