IQ1o. | A. ALcocK : Classification of the Potamonida. 255 
2 ( Mandibular palp of two joints, 
| the terminal joint thickened and 
J plumose at base, but not dis- 
| 
tinctly bilobed i .. DECKENIINA, 
| Efferent branchial channels not thu 
produced Hh : 3 
(Mandibular palp of either two or 
three joints, the terminal joint 
| sometimes thickened and plumose 
é J at base, but not distinctly bilobed. Poramontnai. 
» | Mandibular palp of two joints, the 
| terminal joint deeply cut into two 
| lobes, which embrace the incisor 
process of the mandible 
(Abdomen of adult male usually 
broad at base and suddenly con- 
tracted at the 5th or 6th segment: 
the length of the sixth segment 
often exceeds and seldom falls 
| short of its distal breadth: the 
| seventh segment is almost al- 
44 ways either elongate-triangular or 
os 
tongue-shaped ; 
; .. GECARCINUCINAS (PaRaA- 
Abdomen of adult male not abruptly TELPHUSINA}). 
contracted distally: thes xth seg- 
ment is usually much broader 
than long, and the seventh seg- 
ment is broadly triangular: male 
abdominal appendages heavy, 
with blunt, lobed ends .. PSEUDOTELPHUSIN] 
(POTAMOCARCININA,), 
— 
KEY TO THE SUBFAMILIES OF POTAMONIDA. 
(Terminal joint of mandibular palp 
| deeply cut into lobes which em- 
brace the incisor process of the 
mandible between them pee a 
Terminal joint of mandibular palp 
: consisting of a single lobe (the 
base of which may be sometimes 
| thickened and plumose) lying be- 
hind the incisor process of the 
|. mandible! .. Oe ARTY 
' In some of the Potamonine the thickening of the base of the terminal joint 
of the palp is considerable, and as the hairs that fringe the thickening hang in a 
tuft over the incisor process of the mandible, the whole has somewhat the appear- 
ance of an independent lobe; this condition is most manifest in Potamonautes and 
in some of the African species of Geotelphusa, but it is not difficult to distinguish 
it from the broad, heavy, overhanging lobe of, e.g., Paratelphusa tridentata, it the 
palp be removed and denuded. 
