I910.] J. R. HENDERSON & G. Matruar: Freshwater Prawns. 293 
appears almost convex. ‘This characteristic persists even in certain 
large males; it is specially marked in young individuals from 
Cocanada. The tubercles on each side of the finger ridges, so 
characteristic of adults, are absent in the young. Ina specimen 
measuring 82 mm. the chelipedes are practically equal, and their 
joint-measurements are as follows :— 
ieee > Mite Te) cr hO!pEOr +f... 
With advancing age, the chelipedes become unequal in length, 
the tubercles on the fingers make their appearance, and the 
pubescence appears more fully developed. 
General remarks.—-Nobili has described under the name of 
P. alcocki a freshwater prawn from Pondicherry, of which he was 
able to examine only a single specimen measuring 57 mm. in total 
length and obviously immature. In it the tooth-formula is 2 - the 
two upper distal teeth are placed near the tip and two teeth are 
situated on the carapace. The nature and arrangement of the 
teeth are the same as in the species just described, but we have 
not yet met with a specimen showing only 9 upper rostral teeth, 
although we have examined a considerable number. Nobili’s 
figure of the rostrum shows the upper margin to be straight, 
while in the present species the proximal portion is generally 
slightly convex. The large chelipede, a figure of which is also 
given by Nobili, greatly resembles that of young individuals 
oi our species both in shape and in the relative lengths of the 
joints. Nobili lays stress on the dilatation of the palm in 
P. alcocki, and certain young individuals from Cocanada which we 
refer to P. rudis agree in this respect. 
The following is a comparison of the joint-measurements in 
one of our young specimens measuring 58 mm., and those recorded 
by Nobili in his single specimen which measured 57 mm. in total 
length :— 
ihe m. ©; Dp: fe 
Our specimen... 6 Z ee el, OS, 
Nobili’s specimen 7 12 6°5 25 
While, therefore, it is not unlikely that Nobili’s species was 
based on a young specimen of the one which we have just des- 
cribed from examples at different stages of growth, it is impossible 
to decide the matter definitely, because young individuals of many 
species of Palaemon closely resemble one another. 
The joint-measurements of the large chelipedes of specimens 
at various stages of growth are given on page 294. 
