35O JULIAN D. CORRINGTON. 



vironment. Judging from this ever present condition, these crabs 

 seem to require more than ordinary concealment from the nu- 

 merous foes which prey upon them, and hence this factor may be 

 the determining cause for their association with medusa? in the 

 present case. In this connection it is of interest to point out a 

 certain degree of mutual adaptation on the part of the associating 

 species. Stomolophus has a spacious and deep subumbrellar area, 

 within which its large guest finds snug but ample accommodation ; 

 the marginal aperture allows ready ingress and egress ; the ma- 

 nubrium is deeply grooved and pitted, enabling the crab to easily 

 cling to its steed with great tenacity ; and nematocysts are absent 

 or so poorly developed as to be ineffective. The Libinio, on its 

 part, is admirably shaped so as to conform to the contours of this 

 peculiar residence, the back being strongly convex and the ab- 

 dominal surface slightly concave ; the legs are curved inward and 

 end in sharply pointed tips ; and finally, the mid-dorsal spines of 

 the carapace are well developed and would assist in maintaining 

 the position, especially when the crab was situated in the upper 

 regions of the subumbrella, the site from which all of the nine- 

 teen specimens here recorded were dislodged. 



The writer wishes to acknowledge the assistance of Dr. Waldo 

 L. Schmitt of the United States National Museum, who has 

 kindly provided references and identification checks, by Dr. Bige- 

 low for the medusa and Dr. Rathbun for the crab, at a time when 

 original sources were not otherwise available. Specimens illus- 

 trating this association are deposited in the United States National 

 Museum and in the zoological collections of the University of 

 South Carolina. 



LITERATURE CITED. 



Rathbun, M. J. 



'04 Decapod Crustaceans of the Northwest Coast of North America. 



Harriman Alaska Expedition, 10, p. 176. 

 Weymouth, F. W. 



'10 Synopsis of the True Crabs (Brachyura) of Monterey Bay, 

 California. Leland Stanford Junior Univ. Pub., Univ. Ser., 

 No. 4, p. 42. 



