20 CEYLON PEARL OYSTER REPORT. 



tooth, and alongside of the plate which carries this a thin membrane, which appears 

 to be prolonged backward into a slightly curved lingual representative of the molar, 

 the whole apparatus being somewhat obscured by entanglement with the lower lip. 

 The upper lip is slightly emarginate. 



The curved finger of the first gnathopod shows two minute prominences on the 

 inner margin, and one such prominence is visible on the other limbs, faintly marking 

 the base of the nail, but the feature is not peculiar to this species. The telsonic 

 segment has six spines at the apex. 



Length G millims., breadth 275 millims. 



Locality : The dissected specimen was a male from Jokkenpiddi Paar. Two other 

 specimens, apparently of the same species, were obtained at the south end of Cheval 

 Paar. 



Family: JEGIDJE. 



The accepted genera may be distinguished as follows : 



. fPleon abruptly narrower than perreon. 1. Syscenns, Harger, 1880. 



L Pleon not abruptly narrower than perseon 2. 

 (' First antenna3 with flagellum of not more than six 



joints ; maxillipeds of not more than four joints. 2. Rocinela, Leach, 1818. 

 1 First antennae with flagellum of more than six 



joints; maxillipeds of not less than six joints. 3. sEga, Leach, 1815. 



Syscenus agrees with Rocinela in respect to the maxillipeds. It is now recognised 

 that the Rocinela lilljeborgii described by Bovallius in 1885 is identical with 

 Syscenus infelix, Harger, 1880, but it seems to have been overlooked that Bovallius 

 himself was the first to acknowledge the generic identity, and to point out the 

 probability that Havponyx pranizoides, Sars, would prove to be a young Syscenus 

 (' Bihang till k. Svenska Vet. Akad. Handl.,' vol. 11, No. 17, p. 17, 1887). jEgioclms, 

 Bovallius, is not accepted as distinct from sEga. Acherusia, Lucas, 1849, and 

 Alitropus, Milne-Edwards, 1840, are regarded as synonyms of Rocinela; Pterelas, 

 Guerin, 1836, and JEgacylla, Dana, 1856, as synonyms of JEga. 



Mga,, Leach. 



1815, JEga, Leach, ' Trans. Linn. Soc. London,' vol. 11, p. 369. 



1879, iEga, Schiodte and Meinert, ' Naturhist. Tidsskr.,' ser. 3, vol. 12, p. 334. 



1882, JEga, Haswell, 'Proc. Linn. Soc. N.S. Wales,' vol. 6, p. 11. 



1890, .ffiga, H. J. Hansen, ' Vid.-Selsk. Skr.,' ser. 6, vol. 5, p. 316. 



1897, iEga, Sars, ' Crustacea of Norway,' vol. 2, p. 58. 



In recent years species have been added to this genus by Hansen, Whitelegge, 

 H. Richardson and Norman. Many other references to it may be traced under 

 those given above and in company with those given below for the genus Rocinela. 



In defining the genus Leach laid stress on the ample development of the first two 



