76 TESTACEA. 



issue from around the whole circumference, except at the hinge, which 

 exhibit an active, curving, searching motion, in all directions. 



This animal affixes the narrower portion of the shell, by a white 

 silky byssm, to the upper part of the containing vessel. When active, it 

 springs with great force through the water. 



A specimen survived above four months. It is rare. 



Plate XVII. 



Fig. 4. Peden ohsoletus (P. tigrinus). 



10. Pectunculus pilosus (P. glycimeris). — Plate XVII., Figs. 5, 6, 7. 



Shell of globular aspect ; substance thick, strong ; subject massy and 

 heavy. Might be circumscribed by a circle of two inches diameter. The 

 umbo prominent, is situated a little towards one side. Surface wholly 

 furrowed, with fine hollow lines, from the umbo to the margin. Alter- 

 nate dingy white, purple, and brown patches, are disposed in zig-zag ar- 

 rangement on the surface. Towards the margin the shell seems hairy. 

 Colour of the animal mottled brown. Numerous minute black specks 

 stud the fleshy margin, which protrudes little : unless the lower portion, 

 of white colour, which protrudes farther, and folds downwards, in a large 

 mass, exactly resembling that of the Anodon aronensis, and extending 

 two inches, by three quarters of an inch where thickest. 



This animal remains in absolute quiescence. During four months I 

 was not sensible of it ever making the slightest eftbrt to change its 

 position. 



Plate XVII. 



FiQ. 6. Pectunculus pilosus (P. glycimeris, Linn.). 



6. Margin of the shell, enlarged. 



7. Compartment of surface, enlarged. 



