246 Records of the Indian Museum. [Vol. XIII, 



of the male, the sutures of all the segments are distinct. In m^^ 

 interpretation of its limits, Halicaycinus comprises species with 

 simple rostra as well as those in which it is trilobate or tridentate. 



Lucas's Homhronia,^ suggested as a generic name for Jac- 

 quinot's Hymenosoma depressa^ from the Auckland Is, and Nico- 

 let's Liriopea,^ based on two species from Chili, are generally 

 regarded as synonyms of Halicarcinus, and Dana's Hymenicus* is 

 separated by such slight distinctions that it cannot in my opinion 

 be retained as a separate genus. In describing Hymeniciis Dana 

 says : " In this genus the front has not the three teeth of Halicar- 

 cinus (between which the flexed first antennae are seen), but a 

 simple rounded or trilobate prominence forms the front, and the 

 first antennae are covered. The feet are much longer and more 

 slender than in any of the species of Halicarcinus, seen by the 

 author." On comparing H. yan'ws, the type species of Hymeni- 

 cus, with Halicarcinus planatus, the points to which Dana has 

 drawn attention are readily appreciated. The difference, however, 

 is in reality of very slight morphological importance and is entirely 

 due to the greater development of the front in H. varius, the dis- 

 position and structure of the related parts being as nearly as 

 possible identical. Examination of allied forms shows that a wide 

 variation exists in the form of the front and affords conclusive 

 evidence that the character is of specific rather than generic value. 

 The comparatively great length of the legs in H. varius — the only 

 other point mentioned by Dana — is clearly insufficient as a generic 

 criterion; the external maxillipedes are almost identical in struc- 

 ture with those of H . planatus and, as in that species, the sutures 

 of all the segments of the male abdomen are distinct. 



But though Dana's Hymenicus must, through the characters 

 of its type species, be placed in the synonymy of Halicarcinus, it 

 does not follow that all the species hitherto referred to Hymenicus 

 must be transferred to White's genus. The two Indian species 

 described by Alcock,^ together with four others dealt with below, 

 appear to offer distinctive characters. In most particulars they 

 agree with Halicarcinus, but the external maxillipedes are much 

 more slender, with the ischium conspicuously smaller than the 

 merus; when normally folded they gape widely in the middle line, 

 leaving parts of the underlying appendages exposed (see text-fig. 

 7, p. 259). In the abdomen of the male, moreover, the 3rd, 4th 

 and 5th segments are fused, with complete obliteration of the 

 sutures (see text-fig. 9, p. 259). The rostrum is variable in form, 

 but is normally tridentate or trilobate. 



"I Lucas, in Hombron and Jacquinot's Voy. an Pole Sud, Zool., Ill, Crust, 

 p. 62 (1853). 



2 Jacquinot, Atlas to above, Crust., pi. v, figs. 34-39 (1S42-53) ; Chilton, 

 Ann, Mag. Nat. Hist. ( 7 ), XIX, p. 146, pi. v (1907). It is perhaps doubtful whether 

 this species really belongs to Halicarcinus as here defined, for the grooves on the 

 upper syrface of the carapace are not shown in either of the figures. 



■ S Nicolet, in Gay's Hist, fisicay politica de Chile, Zool., Ill, p. 158 (1849). 



+ Dana, U. S. Explor. Exped., Crust., \, p. 387 (1852). 



5 Alcock, Journ. Asiat. Soc. Bengal, LXIX, p. 388 (igoo). 



