280 Records of the Intian Museum. [VouL. V, 
those examined free spermatozoa were found in the vasa defer- 
entia. In normal males similar conditions were met with, but the 
testes were proportionately larger, and the vasa deferentia more 
coiled. We met with free spermatozoa in a male of P. dubius, 
which measured only 37 mm. in total length, with the chelipedes 
subequal and only about half the length of the body, yet the 
general appearance of this specimen, and more particularly of its 
chelipedes, would have led to the assumption that it was a young 
individual. A specimen of P. malcolmsonii, measuring only 93 
mm. in total length, with chelipedes considerably shorter than the 
body, contained free spermatozoa in abundance in the vasa. defer- 
entia. The spermatozoa of Palaemon have a single process 
springing from a head, the free surface of which is convex, so that 
the whole structure bears some resemblance to an umbrella. 
With regard to the last three forms on our list, P. scabriculus, 
P. dolichodactylus, and P. dubius, we have encountered problems 
of considerable perplexity, and are strongly disposed to think that 
they may all belong to one and the same species. Specimens of 
all three forms of adult male were taken together' in the same 
tanks, along with adult females which appeared to be all of one 
type, and a careful examination failed to reveal any differences 
among them such as one would have expected had there been 
three species. Very young males collected under the same condi- 
tions were also alike, and finally there appeared to be connecting 
links between the three forms of adult male. If our view, which 
amounts almost to a conviction, can be established, we have here 
to deal with a species in which the males exhibit polymorphism, 
and we would hazard the opinion that a number of the so-called 
species of Macrobrachium are based upon similar varieties of male. 
In some of the species there appears to be considerable 
variation in the size of adult individuals. In P. malcolmsonii, we 
have females with eggs ranging in total length from 90 mm. to 
118 mm., and our largest female (one without eggs) measures 133 
mm. In this species we also find males with all the special 
characters developed, from I9t mm. to 230 mm. in length. 
Parasites and commensals are occasionally met with on some 
of the species. A Probopyrus is met with, sometimes abundantly, 
on P. malcolmsonit, inhabiting the branchial chamber of either 
side, and we have found a similar parasite in single specimens of 
P. rudis (right side) and P. scabyiculus (left side). In all cases the 
infected host suffers an arrest in growth, and the male chelipedes 
resemble those of females, an observation which has frequently 
been made with regard to other instances of parasitism in Decapod 
Crustacea. Specimens of P. malcolmsonii, from the neighbour- 
hood of Madras, are occasionally found with the chelipedes, 
carapace, and abdominal terga, covered by algae, and the poly- 
zoon Victorella bengalensis, Annandale. 
In the descriptions which follow the total length of the prawn 
is taken from the tip of the rostrum to the apex of the telson. 
In the measurements of the chelipedes the coxa and basis are not 
