152 Memoirs of the Indian Museum. [Voi,. IV, 



numbers already in use, the term variety being restricted to such cases as conform with 

 Borradaile's definition. 



Turning to the forms that differ from G. chiragra in characters of a more trenchant 

 nature, intermediates being rare or perhaps wholly absent, the first that must be con- 

 sidered is Wood-Mason's Gonodactylus platysoma. No description of this form has ever 

 appeared and its claim to recognition rests solely on the figures published in 1895. 

 G. platysoma may be distinguished from G. chiragra by its broader form and by the size 

 and shape of the terminal part of the raptorial dactylus. The telson, with its narrow 

 carinae and complete absence of lateral teeth on the margin differs markedly from that 

 of any G. chiragra in the collection ; but in this respect the form bears a close resem- 

 blance to certain examples to which Lanchester gave the name of G. chiragra var. acutus, 

 and it is possible that these specimens are identical with those determined by Wood- 

 Mason. Judging from the material in the Indian Museum G. platysoma seems quite 

 sufficiently distinct from G. chiragra to claim recognition as a variety. 



In Atlantic waters G. chiragra is represented by a form known as G. oerstedi, 

 Hansen, which differs from its Pacific relative in the possession of a small additional 

 keel on the inner face of the intermediate teeth of the telson edge. The character is so 

 trivial that for many years it entirely escaped detection, but it seems nevertheless to 

 prevail with the most absolute constancy. I have followed the general consensus of 

 opinion in regarding this form as a distinct species, but some may consider subspecific 

 rank more suitable. 



When describing Gonodactylus acutirostris , Dr . de Man mentions that it is possibly 

 only a variety of chiragra ; but, though it is true that it may eventually prove to be a 

 very abnormal form of that species, it should remain separate pending further informa- 

 tion. In the single known example the antero-lateral angles of the rostrum are much 

 more acutely produced than in any G. chiragra, 1 and on the dorsal surface of the telson 

 the two small tubercles, that are situated close to the anterior margin in all the allied 

 forms, are entirely absent, while the submedian carinae are posteriorly convergent. 

 I have seen no specimen possessing any one of these characters. 



Gonodactylus demani, Henderson, and spinosus, Bigelow, are forms which are dis- 

 tinguishable at a glance from all the preceding by the presence of spinules on the dorsal 

 surface of the telson. Apart from this feature G. demani bears a close resemblance to 

 G. chiragra, from which, however, it may be separated by the shape of the dorsal pro- 

 cesses of the ophthalmic somite and by the height and extreme convexity of the mid- 

 dorsal lobe of the telson when seen in lateral view. The dorsal aspect of the telson 

 presents, moreover, a very distinct and characteristic faciès, for the three dorsal keels, 

 and those which terminate in the submedian and intermediate marginal teeth, are all 

 strongly swollen, and are separated from one another by narrow V -sri aped grooves that 

 form a striking contrast to the comparatively wide interspaces found practically with- 

 out exception in G. chiragra. Lanchester, strangely enough, does not mention this 

 form in his synopsis of the varieties of G. chiragra; he has in fact omitted all reference 

 to it, though he cites the paper by Henderson that contains the original description. 



1 But there is, indeed, no little variation in G. chiragra in this respect. 



