iç)i5-] Fauna of the Chilka Lake : Crustacea Decapoda. 225 



The configuration of the groove parallel to the lateral margin of the carapace, 

 whether simply linear or Y-shaped, affords a useful character in the discrimination 

 of the species. In this respect D. pertinax agrees with D. malabarica, Nobili l ; D. fenes- 

 trata, Hilgendorf 2 ; D. brevitarsis, de Man 8 ; D. sulcata, Forskâl*; and D. affinis, 

 Alcock 6 ; and differs from D. wichmanni, de Man ; D. intermedia, de Man* ; D. 

 clepsydrodactylus , Alcock 6 ; D. profuga, Nobili 1 and D. myctiroides, Milne-Edwards 6 . 



From D. malabarica D. pertinax is distinguished (i) by the sculpture of the middle 

 portions of the carapace and by the presence of a faint transverse groove close to the 

 posterior margin, (ii) by the presence of a blade-like tooth on the dactylus of the 

 chela in the male, by the greater comparative length of the fingers and by the absence 

 of carinae on the lower surface of the palm, and (iii) by the presence of a large 

 i tympanum ' on the upper side of the merus of the last legs and by the proportion- 

 ately shorter dactyli. 



Hilgendorf s D. fenestrata possesses sternal 'tympana', a character which it 

 shares only with D. myctiroides , and the features noticed in Alcock' s key suffice to 

 distinguish the present form from D. brevitarsis, D. sulcata and D. affinis. Nobili 1 

 has drawn attention to the close affinity which exists between the two last named 

 species and, in view of his notes on the variation of D .sulcata in the Red Sea, 

 coupled with an examination of specimens of both species (including the types of 

 D. affinis) I am inclined to agree with his suggestion that D. affinis is merely a syno- 

 nym of Forskâl's D. sulcata. In the largest of Alcock' s types there is a small 

 tubercle on the lower surface of the merus of the chelipedes in the position which the 

 spine occupies in adult D. sulcata. 



Living specimens of Dotilla pertinax are of a pale sandy brown colour, mottled 

 with black, white, dark brown and orange red. The precise colouring is very vari- 

 able; there is often a black gastric spot and, in many cases, an orange cardiac blotch. 

 Behind this blotch there is usually a white spot partly surrounded by a brown or 

 black Y-shaped patch, the posterior limb of which extends to the middle of the 

 hinder margin, which is pure white on either side. The furrow at the upper limit of 

 the side walls of the carapace is always deeply pigmented, black, brown or reddish- 

 orange; the sub-hepatic and pterygostomian regions are closely speckled with black 

 and the epistome is often orange red. The legs are banded with brown and white, 

 the carpo-propodal joint of the first two wa king legs being orange. 



The species constructs burrows in the sand close to the water line; usually the 

 boring is made obliquely and extends to a depth of some six or eight inches. Leading 



1 Nobili, Boll. Mus. Torino, XVIII, No. 452, p. 20, fig. 6 (1903). 



2 Hilgendorf, in van d. Decken' s Reise in Ost-Afrika, III, p. 85, pi. iii, fig. 5 (1869). 



3 De Man, Journ. Linn. Soc, Zool , XXII, pp 130, 135, pi. ix (1888). 



4 Nobili, Ann Sei. nat. Zool. (9), IV, p. 315 (1906). 



6 Alcock, Journ. Asiat. Soc. Bengal, LXIX, pp. 363-368 (1900) and Illust. Zool. 'Investigator'' , 

 Crust., pi. Ixiii, 6gs. 1-3 (1902). 



6 De Man, in Weber's Zool. Ergebn. einer Reise in Niederland. Osl-Ind., II, p. 308, pi. xviii, fig. 8. 



7 Nobili, Boll. Mus. Torino, XVIII, No. 447, p. 22 (1903). 



