

2atà 











Jp§ï 



f .V«;< 



'-o" ■ - J^. 



















t 





'*"- ?>■'* *!,*< 







1915.] Fauna of the Chilka Lake : Crustacea Decapoda. 235 



less conspicuous toothing of the antero-lateral margin of the carapace, by the presence 

 of distinct epigastric lobes and by the proportionately narrower exopod of the outer 

 maxillipedes. 



Females of P. onyx bear a very close resemblance to females of P. dentata ; but 

 in the former the carapace is very much flatter both fore and aft and from side 

 to side, its regions are less pronounced, the frontal margin straighter and the upper 

 border of the orbit much less sinuous. The ischium of 

 the outer maxillipedes is proportionately a little broader 

 and there is only a slight prominence, in place of a 

 tooth, in the middle of the anterior border of the buccal 

 cavern. In females of P. onyx, also, the movable finger 

 of the chela is deeply grooved L , whereas it is almost 

 smooth in P. dentata, and, on the outside of the fixed 

 finger, sparse hairs, absent in P. dentata, are to be found 

 in the position occupied by the dense furry patch in the 

 other sex. 



In the largest adult male the length of the carapace 

 is 14/2 mm. and its greatest breadth 15-6 mm., in the 

 two females the lengths are ii"2 and 8-4 mm. and the FlG - ^.-Ptychognathus onyx, 

 breadths I2'0 and 8 - 8 mm., respectively. .. , , . 



' r J Abdomen of male. 



The colouration is apparently very variable. The 

 carapace of the male was, in life, of a dull greyish-green tone with pale spots and 

 mottled with darker grey and dull maroon. One female was pale olive yellow and 

 the other dull grey, in both cases with a few obscure dark markings. 



Ptychognathus onyx was only found on two occasions in the Chika Lake. Three 

 individuals were taken together in the outer channel on a mud bottom off the village 

 of Mahosa on Barhampur I. in September 1914. The depth was between 6 and 8 

 ft. and the water at the time of their capture was perfectly fresh. In December of 

 the same year two additional specimens were found on the oyster-bed near Manik- 

 patna in water of sp. gr. 1-0125. The species is evidently very scarce; but is prob- 

 ably to be found in the locality at all seasons of the year, enduring changes of salinity 

 varying from fresh to water as salt as that of the open sea in the vicinity. 



As has already been stated, the types and only other known examples of the 

 species were probably obtained at Tavoy on the other side of the Bay of Bengal. 



Genus CAMPTANDRIUM, Stimpson. 



1858. Camptandrium, Stimpson, Proc. Acad. Sei. Philadelphia , X, p. 106. 



1907. Camptandrium, Stimpson, Smithson. Misc. Coll., XL,IX, p. 137. 



19 10. Camptandrium, Rathbun, Danske Vidensk. Selsk. Skrifter (7), Naturvid. og math., V, p. 325. 



This genus, hitherto unrecorded from the coast of British India, was originally 

 placed by Stimpson in a separate family; but its affinities are evidently with the 



1 There is a striking difference between the sexes in this respect. 



