igi5.] Fauna of the CliUka Lake : Crustacea Decapoda. 233 



The species does not as a rule reach a large size in the lake. The carapace of a 

 female of quite exceptional dimensions is, however, 50 mm. in length. Ovigerous 

 females were not found. 



In the Gangetic delta Vavuna litterata is very much more abundant. Ever}' year 

 at the commencement of the monsoon the waters of the Hughli river in the vicinity 

 of Calcutta teem with young specimens in the megalopa stage. The}" occur in 

 myriads in all places where the current is sluggish and the water slightly salt and are 

 particularly abundant in the numberless small creeks and backwaters subject to tidal 

 influence. The fact that we never found such larvae during our survey of the lake 

 is strong evidence that the species does not breed there. 



It appears that Varnna is attempting by two methods to establish itself in 

 fresh water in the neighbourhood of Calcutta and the two modes of invasion iway be 

 described respectively as aquatic and terrestrial. 



The enormous numbers of young produced in the brackish water are borne, 

 either by their own efforts or by the influence of currents to points where the water 

 is almost or quite fresh, at any rate at certain seasons of the year, and though it 

 appears that the species has not hitherto been able to establish itself in fresh water 

 by this means, the attempt is made annually by countless multitudes. The pipes of 

 the Calcutta unfiltered water-supply have been found completely choked by Varnna 

 in its megalopa stage. 



The terrestrial method of invasion is adopted by adults. Almost every year 

 the tank (or artificial pond) in the Indian Museum compound, normally inhabited 

 by a Decapod fauna consisting of Parathelphusa spinigera, Wood-Mason, Palaeinon 

 carcinus, Fabr. , and Palaeinon Limarrei, M.-Edw., is visited by stray individuals ot 

 the species and large specimens have been seen on the banks vigorously warding off 

 the attacks of crows. To reach this tank the crabs must make their way by night 

 through the streets of the city, probably along the gutters. Specimens have also 

 been found in fresh water in other parts of the delta, but there is no evidence that 

 the species has ever established itself permanently in this medium. That it may 

 eventually succeed in its efforts is not improbable, for a number of Grapsidae 

 are known exclusively from fresh water. In the Gangetic delta the change from salt 

 water is perhaps a minor difficulty; the hordes of Potamonid crabs, which already 

 occupy the desired territory, may prove a more formidable obstacle. 



Henderson records the common occurrence of this species at the Ennur back- 

 water, where man}' other species included in the Chilka fauna are abundant; Dr. 

 Annandale, however, was unable to find specimens there in January 1915. 



Alcock ' notes that Varu-na litterata is frequently found clinging to logs of drift- 

 wood in the open sea, a fact which accounts for its wide distribution. The species 

 is known from an area extending from the east coast of Africa to New Zealand, 

 Australia and Japan. 



Alcock, A Naturaliit in Indian Seas, London, p. 75 (1902 



