igi.5-] Fauna of the Chilka Lake : Crustacea Decapoda. 319 



Still younger post-larval individuals, which I believe are correctly referred to 

 this species, differ from those of all allied forms with which I am acquainted in 

 their extremely slender build (text-figs. 36a, b). When very young, about 10 mm. 

 in length, they are pelagic and are transparent with a crimson streak running along 

 the ventral surface involving the whole of the antennules and the telson, but not the 

 other appendages, except to a slight extent the uropods. l They possess two pairs of 

 lateral spines on the telson and the rostrum, which in the youngest individuals is 

 without inferior teeth, reaches a little beyond the eyes. 



Rather larger post-larval specimens still retain their slender build, but are 

 deeply mottled with dark grey and dull green and live among weeds. Both colour 

 and form are doubtless protective, as in Hippolytids of the genus Tozeuma, to which 

 these post-larval Penaeids bear a curious resemblance. When captured they are very 

 conspicuous, for, apart from the attenuated form, their deep colouration readily dis- 

 tinguishes them from other species with which they are associated. These, as a rule, 

 consist of other young Penaeidae, young Palaemonidae and Caridina, all of which are 

 semitransparent and but little pigmented. 



Penaeus carinatus is to some extent a migratory species. I am inclined to think 

 that it ascends estuaries and makes its way into water of low salinity only at those 

 seasons in which it is not breeding. It is practically absent from the Calcutta 

 markets for several of the winter months, the supply for this market coming entirely 

 from brackish water. The pelagic post-larval form, which was common in the Ennur 

 backwater near Madras in January, was obtained in the Chilka Lake only in the 

 outer channel in the salt-water season. The latter non-pelagic stage is not uncom- 

 mon in the vicinity of Calcutta in early spring, but, strangely enough, is not represen- 

 ted in our collection from the Chilka Lake. The pelagic form is apparently carried 

 by the tide well up into the Gangetic delta and settles down in weedy pools and 

 backwaters many miles from the sea, to which the adults annually resort at the 

 breeding season. 



In the Chilka Lake P. carinatu^ was less abundant than some other species of 

 Penaeidae; it was, however, found both in the main area and in the outer channel 

 and occurred in both regions at all seasons of the year. It is certainly able to exist 

 for considerable periods in watar that is quite fresh. 



The species has a recorded distribution ranging from Japan to Karachi. 



Penaeus indicus, Milne-Edwards. 



1906. Peneus indicus, Alcock, Cat. Indian Decap. Crust., p. 12, pi. i, figs. 3, 3«. 



1911. Penaeus indicus var. longirostris , de Man, Decap. 'Siboga' Exped., I, Penaeidae, p. 103 and 

 (1913) pi. ix, figs. 32«, b. 



The variety longirostris, described by de Man, is based entirely on the length of 

 the rostrum and the great degree of variation that Indian specimens exhibit in this 



1 P. gracilis, Dana, U. S. Explor. Exped., Crust., I, p. 606, pi. xl, figs, ja, a', b (1852) is apparently 



i>tpf1 r\n«t--larvn1 form 



related post-larval form 



