6o Studies on Arthropods. I. 



specimens in the Copenhagen Museum is from near 200 

 fathoms. 



Another species of the same genus is A . bispinosus A. M.-Edw., 

 which is described and figured by A. Milne-Edwards and Bouvier 

 in Memoirs Mus. Comp. Zool. vol. XXVII, no. i, 1902, p. 127; 

 the specimen was taken in 140 fathoms. Fig. 6 on pi. XXV in 

 that work represents the inner side of a chela and shows a striated 

 vertical area not mentioned in the text; this area agrees much 

 with that found in A. Alexandri, and accordingly A. bispinosus 

 has a stridulating organ completely as developed as in the other 

 species. 



III. Organs and their use in the genus Ocypoda. 



Though the organs found in various species are well known 

 and even afford excellent specific characters, it is necessary for 

 the following considerations to mention two main types. At 

 least 14 species of this genus are accepted as valid, and a 

 stridulating organ is found in all excepting a single form. In 

 this genus the part acting as fiddle is always found in both 

 sexes on the inner side of the large chela, and that area is rubbed 

 against a ridge on the lower side of the ischium of the same leg. 

 In the American 0. quadrata F. a robust, sub vertical keel is 

 found somewhat before the fingers, and this keel has a rather 

 low number of coarse and regularly but not closely set granules; 

 0. platytarsis H. M.-Edw. from India shows a rather similar 

 structure. In the Asiatic 0. macrocera H. M.-Edw. the keel is 

 somewhat low, flattened above, with the lower half of its surface 

 moderately broad, the upper half tapering to the end. Near 

 the upper end this area has rather coarse ridges moderately 

 distant from each other; from the upper end downwards to 

 beyond the middle the ridges become gradually finer and more 

 closely set, and on the lower third they are very fine, and the 

 impressions between them extremely narrow. In the common 



