134 ILLUSTKATIVE 



having adliered to whicli, the lateral expansions creep 

 along the shell, following its surface until they have 

 surrounded the aperture, and meet each other on the 

 outer lip. Here the meeting edges unite by mutual 

 adhesion, and seem to grow together ; yet the suture is 

 always distinctly visible, both by a slight depression, 

 and by a pale line which assumes a zigzag form, 

 owing to the terminations of the body-strise fitting 

 into the interspaces of the opposite ones. 



What is curious in the case is the instinct which 

 makes the Adamsia select a shell as its constant 

 support, and the association with it of a Hermit Crab 

 as the co-tenant of the same shell. This association 

 is, I think, constant ; for, though the dredge does 

 occasionally bring up shells invested by the Adamsia^ 

 which are empty, yet I incline to believe that these 

 shells have been recently vacated by the tenant 

 Crabs, and not that they have never been so occupied 

 at all. 



That the above is the coiTect explanation is evident 

 from specimens in various stages of development. 

 There is in my possession, while writing this note, 

 an Adamsia^ adhering to a Whelk, of which the lateral 

 lobes, though projected around the edges of the mouth 

 of the shell, have not yet met each other on the outer 

 lip, but are separated by a space of a quarter of an 

 inch. And my friend Mr. Thompson, whose oppor- 

 tunities for studying the marine animals of Dorset- 

 shire have been zealously improved, has just showed 

 me a very young specimen, not larger than a silver 

 threepence, in which the side lobes were not in the 

 least developed. This specimen had selected a land 



