ig8 Memoirs of the Indian Museum. [Voi,. IV, 



burrows itself and his observations are, as a rule, so accurate that one hesitates to 

 suggest that he may in this instance have been misled. 



The source of the noise made by the species of Gonodactylus seems never to have 

 been adequately described. In the case of G. glabrous and G. demani, and doubtless 

 with other species of the genus also, it is caused by the raptorial claws when these 

 limbs are used for offensive or defensive purposes. When a living specimen is seized 

 the distal end of the raptorial propodus is fitted into the socket hollowed in the 

 merus for its reception, and while still lodged in this socket muscular effort is brought 

 to bear. Then by a slight alteration in the relative positions of the mero-carpal 

 and carpo-propodal joints the propodus is suddenly released and flies straight out in 

 front. The dactylus, which before the release of the propodus is flexed close against 

 that segment, also flies forwards so that all the segments of the limb are momentarily 

 extended as nearly as possible in a straight line. The action takes place with great 

 rapidity and is in consequence somewhat difficult to observe ; it is roughly com- 

 parable to a rapier-thrust and a well-grown specimen might, I believe, under favour- 

 able circumstances succeed in piercing the skin of the hand. 



The sound appears to be produced by the release of the propodus from the 

 socket in the merus. In all probability it is merely a subsidiary result of the mecha- 

 nical process involved ; it is not so loud as that made by the Alpheid Macrura, and is 

 no doubt less effectual in frightening an opponent. 



Gonodactylus demani, Henderson, [p. 164.] 

 This species was not uncommon both at Kilakarai and Pamban , occurring in the 

 same situations as G. glabrous. It was in an adjacent locality that Dr. J. R. Hen- 

 derson in 1889 obtained the specimens from which he drew up the original descrip- 

 tion of the species. 



A curious feature of all the specimens collected is that the setae on the inner 

 margin of the inner uropod are absent. In all other examples of G. demani in the 

 Museum collection, with the exception of one from the Henjam Is., Persian Gulf, 

 the entire margin is invested with setae. The absence of these setae is clearly shown 

 in Henderson's figure of the type specimen, and on careful examination of the speci- 

 mens recently obtained, it is evident that their absence is not traumatic, as no trace 

 of the pits from which the setae arise can be detected. 



The character no doubt appears somewhat insignificant and the evidence at 

 present available is not sufficient to permit of any suggestions regarding the possible 

 existence of local races : the specimens in the Indian Museum prove that both forms 

 occur in the Persian Gulf. Considering, however, the differences of opinion that 

 prevail regarding the status of the species in the chiragra section of the genus, it is 

 well to place on record any definite character such as that noted above ; and in the 

 present instance a considerable amount of interest attaches to the disposition of the 

 setae l on the uropod in view of the fact that the form of this segment and its setal 



1 It may be mentioned here that in the specimens from Ceylon which I have referred to G. demani 

 var. spinosus the setae invest all the margins of the inner uropod. 



