22 CRABS FROM TITE INDIAN OCEAN— M. J. RATHBUN. vol.xvii. 



rior ridge stojjping sLort of the inner margin, the posterior ridge shorter 

 and not reaching the onter margin. The surface of tlie abdomen and 

 sternum is covered with bead-like tubercles except for irregular eroded 

 channels or pits. The right cheliped (the left one is missing) is massive 

 and tuberculous or spinous. The merus is short and thick, margins 

 tuberculous, inner and outer surfaces smooth, lower surface linely tuber- 

 culous. Carpus with lower half of outer surface spinous. Manus with 

 upper surface subtriaugular, half as broad as long; outer surface with 

 longitudinal spinous ridges, two of which are continued on the pollex 

 and terminate in two of the five strong teeth (one is terminal) of the 

 prehensile edge. The dactylus bears four spinous ridges on its outer 

 and upper surface and seven teeth on the prehensile edge which are 

 smaller than the propodal teeth and fit closely into the spaces between 

 them. The inner surface of the manus is tuberculous on its proximal 

 lower portion. The ambulatory legs are short and broad; the last two 

 pairs when drawn up, fit into the cavity adjoining the posterolateral 

 border of the carapace. The meral joints are very broad (in the first 

 pair the width is one-half the length), and are hollowed beneath to 

 receive the tvv'o following joints; their anterior distal angles are i)ro- 

 duced and rounded. The distal end of the propodus is much broader 

 than the adjacent portion of the rather slender and slightly tapering 

 dactylus. 



Unfortunately it is impossible to give an accurate description of the 

 natural color of the specimen, as with other crabs it was placed when 

 collected in contact with nudibranch mollusks, which have given it a 

 diirk blackish-blue color. ,, (The entire surface is ^ coated Avith a menir 

 branous covering apparently epidermn; which tends to obscure the 

 tubercles. Where this has been removed with muriatic acid the cara- 

 liace appears to be blotclied with bright red and white. The tips of 

 the spines are white. The carapace is sparingly hairy, the legs are 

 margined with hair, and the subbranchial regions are very hairy. 



Measurements. — Length of carapace (of male), 55.5 mm.; width, 70; 

 length of manus, lower margin, 44; depth, 1*1; width of upper surtace, 

 10; length of merus of last ambulatory leg, upper margin, 10.5; length 

 of carpal joint, 11; length of propodal joint, 0; length of dactylus, 10; 

 width of merus, 0.5; proximal width of j)roi)odal joint, 0; distal 

 width, 4; greatest or transverse diameter of pterygostomian cavity, 

 25; opx)osite dimension, 11. 



Locality. — Aldabra Island. (One male, No. 17753). 



A. Milne-Edwards in describing the genus* says that the pterygo- 

 stomian cavity is concealed by the anterior feet when the latter are 

 folded against the carapace. This is not the case in this species. 

 In no position does the clieliiied fit tightly over the cavity. When the 

 cheliped is folded, the u])per surface of the manus is continuous with 



*Nouv. Arch. Mus. Hist. Nat. Paris, i, 1865, p. 295. 



