MARINE CRUSTACEANS. 447 



Turning now to the different varieties of G. chiragra, as now defined, afforded by this 

 collection and the accounts of earlier authors, I must premise that I find it necessary to 

 deal with them under three headings, the first two concerning those varieties which connect 

 with each other by greater or lesser transitions of structure, the third concerning those which 

 do not fall so readily into a transitional scheme. It will be easily understood that by the 

 very nature of the case the exact definition of the different varieties must be a matter of 

 considerable difficulty, that it would be open to any other observer, by a re-shuffiing of the 

 cards, so to speak, to form a scheme differing, in detailed arrangement, from the one now 

 given, and that such a scheme cannot pretend as yet, while the material, and the information 

 on this material, are still so comparatively limited, to represent with any certainty the genetic 

 history of the forms in question. 



First heading. I. Var. tumidus var. nov. PI. XXIII. figs. 1 and 1 a. 



This is that form of G. chiragra which has been taken by most carcinologists to be 

 the type of the species, in which there are three much swollen carinae, without spines, on 

 the telson, and no lateral marginal teeth. To this should be referred the examples described 

 or figured by Herbst, Milne-Edwards (partim), Dana, von Martens, Miers, Brooks, Henderson, 

 Bigelow, Borradaile. Although the absence of the lateral marginals is characteristic of this 

 variety, yet sometimes traces of these teeth may be seen, as Jn the case of Fig. 1, and 

 it is worth noting that the tooth is more prominent on the one side than the other; in 

 a second specimen the teeth are absent, and in a third the rudiments of teeth are equal. 



3 (/(/"> length 61'5, 48"5, and 44"5. Minikoi; with the following note: — "variegated green 

 and white. The dark patches on the last thoracic segment and 5th abdominal segment are 

 very characteristic ; latter orange-red in centre." From the reef. 



II. Forms connecting var. tumidus with III. var. acutus. PL XXIII. fig. 2. 



The carinae are distinctly less swollen, especially the median. No lateral marginals. 

 1 /, length 42-5, and 2 ? ?, 50 and 43, Minikoi. From the reef 



III. Var. acutus var. nov. PI. XXIII. figs. 3 and 3 a. 



The three carinae are now sharply defined, and the distal end of the median carina drops 

 almost vertically so as to appear angular, rather than rounded and sloping as in var. tumidus. 

 No lateral marginals. 



3 % %, length 38'5, 37, and 39, Minikoi, with the same note as that applying to the 

 specimens of var. tumidus, and 2 $ $, length 62*5 and 15, Minikoi. From the reef 



IV. Var. smithii Pocock. PI. XXIII. figs. 4 and 4 a. 



Carinae sharp, the median with a well-defined terminal spine. Lateral marginal teeth 

 present. 



1 (/", length 22, Hulule, Male Atoll, Maldives. From the reef 



To this form belongs a specimen referred by me to var. smithii Pocock in the Proc. 

 Zool. Soc. London, 1900, p. 555 ; also three specimens referred by Borradaile to the same variety 

 from Rotuma. In the latter's examples there are no signs of backwardly-directed carinae 

 proceeding firom the base of the spine of the median carina; in my two specimens, however, 

 these can just be seen (cf fig. 4), and this form clearly leads on to 



