MARINE BIOLOGICAL STATION AT PORT ERIN. 



117 



which can be protruded from the anterior end of the shell 

 for a considerable distance. The mussel {Mytilus edulis), 

 see fig. XXII., and various kinds of Venus and Tapes are 

 common at Port Erin. No 3 is the curious little slug- 

 like Mollusc, Chiton Icevis, frequently found under stones 

 and in pools, and quite exceptional in having the shell 

 represented by a series of eight pieces arranged along the 



manfl 



8 t 



siphon 



%,.4- : - ' " bvssi 



Fig. XXII. — Mytilus edulis, the Common Mussel (natural size.) 



back like a series of overlapping tiles. This leads to the 

 ordinary univalves (Gastropoda), of which we have an 

 example in the common dog-whelk (Purpura lapillus) 

 at 4 on fig. XXI. These animals have a broad creeping 

 " foot," like that of the garden snail, with the head and 

 mouth in front and the tail behind. The spirally coiled 

 univalve shell is balanced on the back, and all can be 



