202 SMITHSONIAN MISCELLANEOUS COLLECTIONS 



and with its superior margin armed with sharp spines. Ambulatory 

 feet slender, overreaching the chelipeds ; antepenult joint with den- 

 ticulated margin ; penult nearly smooth above ; dactylus hairy, com- 

 pressed, and, as usual, sulcated. Length, 1.25; length of carapax, 

 0.29; breadth of front, 0.135 ; length of great cheliped, 0.45 inch. 



From D. custos, which it resembles in the character of the greater 

 cheliped, this species differs in its shorter rostrum and the smooth 

 superior surface of the penult joint of the ambulatory feet. 



Dredged in twelve fathoms on a sandy bottom in Simons Bay, 

 Cape of Good Hope. 



314. DIOGENES EDWARDSII (De Haan) Stimpson 



Plate XXIV, Fig. i 



Pagnrus cdi^'ardsii De Haan, Fauna Jap., Crust., 21 r, pi. l, fig. i. 

 Diogenes edzvardsii Stimpson, Proc. xA.cad. Nat. Sci. Phila., .\, p. 246 

 [84], 1858. 



The ophthalmic rostrum is minute and very narrow, scarcely per- 

 ceptible to the naked eye. The acicle is short, triangular, and spin- 

 ulose. Genital apertures of the male on the inner surface of the 

 coxae. In living specimens the carapax was of a pale red color ; feet 

 annulated with pale reddish brown ; larger hand white ; abdomen 

 yellow, with pale-red sides. Our largest specimen is one and one- 

 half inches in length. 



In De Haan's figure the dactyli of the ambulatory feet are repre- 

 sented too short and very much too broad ; they are in reality ver\" 

 long and slender, one-half longer than the penult joint. 



In this species we have another instance of the economic relation 

 which we so often see existing between a crustacean and a polyp. 

 Upon the outer surface of the greater hand, in all the specimens 

 we have seen, there is seated a small species of actinian. That 

 this is not accidental, we infer, not only from the occurrence of 

 the polyp tipon all our specimens of the crab, and its non-occur- 

 rence elsewhere, but from the fact that there is a special adapta- 

 tion of the outer surface of the hand to receive such a parasite ; it 

 has a smooth, oval area occupying two-thirds of the surface, and 

 partly surrounded by an elevated ridge. The polyp undoubtedly 

 derives much advantage from this position, so near the food-seizing 

 members of the crab — certainly enough to compensate for any hard 

 knocks its tough body may receive ; but what advantage may inure 

 to the crab is here less perceptible than in the case of Cancrisocia 

 and Dorippe. The surface of the claw to which the polyp is at- 



