170 Memoirs of the Indian Museum. [Voi<. IV, 



tional groove, running almost longitudinally and situated midway between the lateral 

 margin, and the commencement of the transverse groove. 



The presence of these grooves (see text-fig. 1), though the only constant charac- 

 ter by which G. graphurus may be distinguished from its ally, is, I believe, a feature 

 of sufficient importance to justify specific separation ; intermediate specimens appear 

 to be wholly unknown. Pocock (1893, p. 475) notes that in a semi-larval form, 10 

 mm. in length, the grooves are found only on the fifth abdominal somite, but that 

 in all the other numerous examples which he examined, they were well-marked without 

 sign of failing. 



Fig. 1. Gonodactylus graphurus 

 Fig. 2. Gonodactylus glabrous 



First five abdominal somites viewed laterally. 



A fine median carina is usually — perhaps invariably — found on the sixth abdo- 

 minal somite, but this character is shared by some examples of G. glabrous. 



The other keels on the last abdominal somite and those on the telson appear to 

 vary in precisely the same way as in the preceding species. In the two examples from 

 Port Molle they are slender, but moderately swollen in the third specimen ; in all three 

 the median and submedian keels of the telson terminate in spines. 



The colouring of living G. graphurus is doubtless as variable as that of its allies. 



There are only three specimens in the Indian Museum : — 

 -y- Australia. Queensland Museum. 1 J , 60 mm. 



^ Port Molle, Queensland. Australian Museum. 1 $ , 1 ? , 35, 40 mm. 



Both in Henderson's experience and in my own, G. glabrous occurs on the coasts of 

 India to the complete exclusion of G. graphurus, and it would naturally be expected 

 that, in the case of the latter species, further indications of a geographical range more 

 limited than that of G. glabrous would be found in the published records. It is not 

 altogether clear, however, that this is so. The head-quarters of G. graphurus appear 

 to lie in an area comprising Oceania, the N. coast of Australia, Amboina and the China 

 Seas, but from certain isolated records from the E. African coast, it would seem that the 

 species is in reality distributed over the whole Indo-pacific region. 



As regards the African records it will be noticed that Nobili, writing towards the 

 end of 1906,, includes in his synonymy of G. glabrous, his record of G. graphurus from 



