128 SAGARTIAD.E. 



shell. This process invariably begins at the suture, and as 

 it goes on the suture divides, the lateral portions separating 

 more and more from each other by shrinking ; thus reversing 

 the steps by which the annular habit was assumed. 



So far as my own experience goes, the Adamsia always 

 selects for its support the inner lip of a turbinate shell. 

 Buccinum undatum I have generally seen chosen at Wey- 

 mouth, but not rarely the various species of Trochus ; and 

 a Helix I have already mentioned : Adams found it at 

 Milford Haven, on Murex despectus (= Fusus antiquus) : 

 Thompson, at Belfast, on Bulla lignaria, as well as on the 

 larger Trochi : E. Forbes, at the Isle of Man, on old Fusi 

 and Trochi: Landsborough, at Arran, on Turritella and 

 Buccinum. Mr. D. Robertson sends me specimens from 

 Cumbrae, on Trochus umbilicatus. 



I believe that the shell chosen is always tenanted by a 

 Hermit Crab, and that the species is invariably Pagurus 

 Prideauxii. In this my observation coincides with those 

 of Dr. Coldstream, Thompson of Belfast, and Mr. D. Ro- 

 bertson. Forbes seems to throw doubt on the constancy of 

 this association ; having taken many specimens on the Manx 

 coast, the shells of which were not tenanted by any crab. 

 Similar examples have occurred to myself at Weymouth ; 

 but when we remember how readily the Pagurus leaves its 

 shell on alarm, and how terrifying the rough action of the 

 dredge-iron must be, it seems the most obvious mode of 

 accounting for the occasional vacancy of the shell, that it 

 has been just deserted by its frightened tenant. 



The Adamsia itself in early life has the power of shifting 

 its quarters. Forbes observes that it " seems to change its 

 habitation according to its size : " and I have had two 

 young specimens in my aquarium, which crawled sponta- 

 neously from their shells, and attached themselves the one 

 to a stone, the other to the frond of a sea-weed. While 



