384 Records of the Indian Museum. [Vol. XVI, 



Unfortunately it is not at present possible to include Euplax 

 definitely in the synonymy of Macrof)hlhalmus, for E. hptophthalma 

 from Chili, the type species of the former genus, has never been 

 re-examined since Milne-Edwards described it ; there is thus a 

 possibility that it may possess characters, hitherto overlooked, which 

 entitle it to generic recognition. There is, however, very little 

 doubt that E. &osc/ must be regarded as a species of Macrophthalmus, 

 to which genus both Audouin and Krauss referred it. In his notes 

 on the species Tesch remarks ' that the proportional length of the 

 merus of the outer maxillipeds in relation to the ischium is vari- 

 able. This variation also extends to the relative length and 

 breadth of the merus ; the segment is sometimes nearly as long as 

 broad, sometimes as much as one sixth broader than long. In this 

 respect it is not possible to draw a distinction between E. hosci and 

 such species as Macrophthalmus erato and M. pacificus. 



E. hosci, moreover, as Tesch has noted*, is so very closely 

 related to Macrophthalmus crinitus, Rathbun, that the two forms 

 can only with difficulty be distinguished from one another (see p. 

 391). There can be no possible doubt that the two species are 

 congeneric, yet no one has suggested that M. crinitus should be 

 referred to Euplax. In both species the gape of the outer maxil- 

 lipeds is a little wider than in normal M acrophthalmus and the 

 front proportionately broader. But the former distinction is a 

 trivial one and the difference, on comparison with M . pacificus, is 

 very small ; in the latter the species merely takes a place at one 

 end of an evenly graded series. 



The position of the Australian species, described by Milne- 

 Edwards as Cleistostoma tridentatum and recently referred to the 

 genus Euplax by Miss Rathbun and Tesch, seems to require further 

 investigation. On comparison with Hemiplax hirtipes from New 

 Zealand I find mam^ points of resemblance. The two species agree 

 with one another and differ from all normal species of Macroph- 

 thalmus in three characters : — (i) the front is extremely broad, its 

 breadth between the eyestalks being considerably more than one 

 third that of the carapace, (ii) the sides of the front are strongh^ 

 convergent anteriorly, and (iii) there are no enlarged teeth on the 

 fingers of the male cheliped. It appears to me therefore that C. 

 tridentatum should be referred to Heller's Hemiplax; but the dis- 

 tinctions between this genus and Macrophthalmus are by no means 

 convincing and it will perhaps be better to regard the former 

 merely as a subgenus of the latter. 



At the present moment two broad-fronted Australian species 

 of M acrophthalmus , M. punctulatus , Miers and M./a^z^'/raws, Has well, 

 are known to us only from the original descriptions. When these 

 have been rediscovered we shall probably be better able to decide 

 on the position of C. tridentatum and on the validity of Hemi- 

 plax. 



I Tesch, loc.cit., t()i8, p. 6n. "' Tesch, loc. cit., 1915, p- IQ2. 



