138 A. R. Anderson — Sound produced by the Ocypode Crah. [No. 2, 



Nahtral History Notes from the Royal Indian Marine Survey Steamer ' In- 

 vestigator,'' Commander C. F. Oldham, R. N., commanding.— Series 

 IL, No, 12. Note on the sound produced by the Ocypode Grab, Ocypoda 

 ceratophthalma. By Surgeon-Captain A. R. Anderson, B.A., M.B. 

 Naturalist to the Indian Marine Survey. 



[Received and Read 4th July.] 



Although in several Brachyurous Decapod Crustaceans stridulatino- 

 ridges have been most carefully described and figured, in only one 

 solitary instance can I find any observations regarding the sounds 

 produced by these ridges. Indeed they appear to have derived their 

 designation rather from the resemblance they bear to the stridulating 

 organs of insects than from any stridulating function they themsel i^es 

 had been observed to possess. In this note I venture, therefoi'e, to describe 

 the sound produced by the -vvell-known stridulating organ of Ocypoda 

 ceratophthalma, Pallas, a description of Avhich, as well as of the ridges 

 foimd in such other species of Ocypoda as possess them, will be found 

 given by Miers in the Annals and Magazine of Natural History Vol. 

 X, 1882. Dana, in the volume describing the Crustacea of the United 

 States Exploring Expedition, writes of the genus Ocypoda: — "These 

 species are able to make a sound, by means of a series of minute rido-es 

 on the inner surface of the hand, which acts like a rasp against a promi- 

 nent edge on the second joint of the same pair of legs." He however 

 gives no description of the sound produced. In the Administration 

 Report of the Marine Survey of India for 1891-92, Surgeon- Captain 

 A. Alcock relates his experiences of the musical powers of tlie red 

 Ocypoda macrocera, and with this solitary exception, I am unable to 

 find any record of similar powers having been obsei-ved in any other of 

 the Ocypodes. 



In Ocypoda ceratophthalma the stridulating organ consists of a 

 ridge coarsely striated above, finely striated below, borne on the inner 

 surface of the hand of the larger chela. This ridge is rubbed across a 

 smooth raised ridge on the ischium of the same chela, and by slowly 

 rubbing the opposed ridges together, and placing the crab over the 

 mouth of a wide-necked bottle to act, like the crab's buiTow, as a 

 resonator, an exact reproduction of the soiind emitted by the crab 

 dui'ing life, can be obtained. One bright hot sunshiny morning in Nov- 

 ember, as I was walking along the shore of Bingaroo, one of the Lakadive 

 Islands, which is only occasionally visited by the inhabitants of the 

 other islands of the same atoll, I was surj^rised to hear a loud croak- 

 ing noise, that appeared to proceed from the edge of the scrub juno-le 



