Crustacea Decapoda and Stomatopoda. 
241 
Though the two forms are clearly allied there are many conspicuous differences 
between these young individuals and S. foxi. The carapace is decidedly broader than 
long and its lateral margins are posteriorly divergent. The orbital tooth is narrower, 
the first epibranchial tooth more prominent and a strong ridge runs obliquely inwards 
and backwards from the rudimentary second epibranchial tooth. The walking legs 
are much stouter, the merus of the penultimate pair being scarcely more than two 
and a half times as long as broad. 
It is possible that these are young examples of the form described by lyanchester 
from "Lacom" and Bukit Besar as Sesarma maculata, de Man, but they differ notice- 
ably from de Man's description, especially in the form of the penultimate segment of 
the male abdomen. It appears to me exceedingly improbable that the true S. macu- 
lata, which was described from Flores, can occur in the Malay Peninsula. 
Sesarma politum, de Man. 
1888. Sesarma polita, de Man, Journ. Linn. Soc, XX, p. i8g, pi. xiii, figs. 7-9. 
Three specimens were found at the mouth of the Tale Sap on the shores of Kaw 
Deng. The largest is a female with carapace 21 5 mm. in length. In the smallest 
the carapace is only 7-5 mm. long and the second epibranchial tooth is undeveloped. 
Genus H el ice, de Haan. 
Helice tridens, de Haan. 
1894. Helice tridens, Ortmann, Zool. Jahrb. Syst., VII, p. 727. 
A single male, with carapace 26 mm. in breadth, was presented to Dr. Annandale 
by Prof. S. Yoshida. It was obtained in brackish water near Osaka in Japan. 
Genus Clistocoeloma, A. Mihie-Edwards. 
Clistocoeloma merguiense, de Man. 
1900. Clistocoeloma merguiense, Alcock, Journ. Asiat. Soc. Bengal, LXIX, p. 429. 
Two specimens, a male and a female, were obtained by Dr. Annandale in fresh 
water near the mouth of the Patani River in the Siamese Malay States. The cara- 
pace of the male is 8-3 mm. in length and 9-4 mm. in breadth ; that of the female is 
9 9 mm. in length and 11 -8 mm. in breadth. The specimens were found in burrows in 
wet mud, under the trunk of a dead palm tree. 
Family POTAMONIDAE. 
In determining the ten species of river-crabs in the present collection I have 
followed the classification proposed by Alcock in 1910.' Alcock divides the family 
into two groups, the Potamoninae and the Gecarcinucinae, mainly on characters 
drawn from the structure of the mandibular palp. In the former subfamily the ter- 
minal segment of the palp is " simple, sometimes thickened at the base for the attach- 
ment of a bunch of hairs," whereas in the latter it is " cut into two lobes which em- 
1 Alcock, Cat. Indian Decap. Crust., I, fasc. ii, p. 17 (1910). 
