Molluscs. 



flapping movements. The body is brigiitly coloured, some of 

 tlie organs being of a ^^^•'id (grange ; tlie foot is small and of no 

 service in locomotion ; the margins of the mantle are frilled, 

 and bear a row of conspicuous black ej'es of considerable com- 

 plexitv, in relation, no doubt, vdth the active habits of this 

 mollusc. Pecfen opercularis and P. Vdrkis are smaller species, 

 the latter rarely exceeding one and a half inches in width, 

 and var-sdng in colour from whitish to bright yellow, orange or 

 red. The scaUops are hermaphrodite. 



The Pelecypods further include various moUuscs which, owing 

 to their powers of excavation, cause considerable damage to 

 wooden piles, and even the stone\\'ork of piers and jetties (Fig. 32). 

 Such borers have usually taken on a somewhat worm-like shape, 

 though retaini)!g the bivalve shell. The Piddock or Stone- 

 borer (Pholas dactylics) is common, and considered an excellent 

 bait for certain fishes (Fig. 33). Its shell is thin and brittle, of a 

 pure white colour, and gaping at each end, the siphons project 

 behind and the foot in front. The siphons are long and stout, and, 

 being united along their whole length, contribute to the animal's 

 vermiform appearance ; the foot is short and truncated, and 

 probably acts as the chief excavating organ, although the sharp 

 and rasp-like edges of the shell serve to supplement its action. 

 The Piddock can bore not only in chalk and limestone, but 

 even in slate and other except the very hardest rocks, making 

 tubular excavations exposed at low water. Dr. Murie describes 

 these molluscs as common at the base of the chalk chffs near 

 Margate and in the neighbourhood of Dover ; the blocks of 

 stone forming the Folkestone pier are also said to be full of 

 holes tenanted bj' Pholas. 



The Ship-worm {Teredo navalis) is a still more remarkable 

 bivalve, extraordinarily destructive to timber in many distncts 

 (Fig. 33). Vermiform and from six to twelve inches long. Teredo 

 would scarcely be recognised as a mollusc were it not for the 

 small shell-valves at the anterior extremity, much too small to 

 shelter the whole animal, which therefore secretes a thin supple- 

 mentary' shell round the tube-shaped body. The worm-like 

 shape is due largely to the great elongation of the fused siphons. 

 The shipworms excavate long parallel galleries in almost e\'ery 

 kind of timber, thus causing serious damage to wooden ships, 

 piers, etc. The boring is performed by the sucker-like foot, 

 and the debris are ejected by the respiratory current through 

 the exhalent siphon. 



In concluding this brief survey of our bivalve molluscs, it 

 may be well to advise the amateur naturalist to pay more 



