178 CRUISE OF THE BARRERA 



In all of our dredging operations we encountered 

 hermit crabs of many species. Probably no sin- 

 gle group of animals of as high rank in the biologi- 

 cal series displays a wider range of adaptation 

 to special life conditions than do the Pagurids. 

 Many species appear to have chosen some par- 

 ticular mollusk-shell for their abodes, and in order 

 to fit comfortably within they have altered their 

 "figures" in most surprising fashion. One case 

 coming under our observation is especially note- 

 worthy — the Pylopagurus discoidalis which has 

 adapted itself, or better, "fitted" itself, to the 

 long narrow confines of a Dentalium shell, the entire 

 body having straightened and elongated itself out 

 of all semblance to the usual hermit's shape, and 

 one claw has become beautifully modified to 

 serve as an "operculum" or trap-door which per- 

 fectly closes the shell aperture. This modifica- 

 tion of the claw is no rough amateurish job but 

 is a perfect accomplishment even to the minutest 

 details of what a protecting cover should be. 

 Aside from the wide range of their interesting 

 evolutionary changes, the Pagurids offer still 

 more of interest to the nature student. They are 

 such restless nervous little beasts, so pugnacious, 



