PHOTOTYPE PLATE NO. XXIX. 



45 



coral rock by a byssus, of such size and strength that the aid of an axe is required to release 

 it from its moorings. As a matter of fact, these Clams, in their adult condition, possess neither 

 byssus nor other anchoring ligament, but lie entirely free on the surface of the reef. Similar 

 growth-conditions obtain also in the case of the smaller spotted or Bear's-foot Clam, Hippopiis 

 iiiacitlatus, that abounds on the same reefs; it being only the more ornate Frilled, or Furbelow, 

 Clam, Tridaciia coiiipirssa, that is permanently attached. The anchoring cable in this species, more- 

 over, is not a bundle of thread-like filaments, or " byssus," of the more familiar type, but rather 

 a solid fleshy, cartilaginoid plug. The colours of the mantle membranes, conspicuously visible 

 between the slightly gaping valves, in the living animal of the Giant Clam, are by no means 

 brilliant, like those of the last-named species, being almost invariably light-brown, with trans- 

 verse streaks of a darker hue of the same tint. From the references made to this species, 

 Tridaciia gigas, in many natural-history works, and accounts of voyages of discovery, including 

 Jukes' "Voyage of H.M.S. Fly," Vol. I., p. 6, it is very evident that the permanently attached 

 and most commonly coral-embedded Tridaciia co/iiprcssa has been mistaken for the young of 

 its gigantic relative. Under the title of "Gigantic Cockles," these Barrier Reef Clams were 

 first recorded by Captain Cook (" First Voyage Round the World," Vol. II., 1821), who 

 attests to their excellent edible properties. Where, however, so many other shell-fish abound, 

 of more tender and delicate substance and flavour, these colossal bivalves are, except by the 

 natives, held in very little account. A considerable trade is, at the same time, carried on 

 with the ordinary large-sized shells, which are obtained chiefly by the Beche-de-mer fishers, 

 and retailed for decorative purposes at an average rate of jli a pair. 



A brief examination of the reef-scape now under discussion will reveal the presence of two 

 other large Tridacn^, a little more towards the background, on the same side of the picture. 

 This suffices, to some extent, to indicate their gregarious habits. These more remote speci- 

 mens have much younger, smoother, shells than the foreground example, and exhibit very 

 distinctly their typical fluted contour. In the case of the older shells, it not unfrequently 

 happens that they are so thickly encrusted with corals, sponges, and other marine growths, that 

 their real identity is almost completely disguised. It is under such conditions that they un- 

 doubtedly constitute a formidable source of danger to those whose calling necessitates spend- 

 ing the greater portion of their days in collecting the highly valuable commercial products of the 

 reefs, by wading or diving. A foot inadvertently inserted betwixt the gaping valves of a large 

 Tridacna is held with a grip as firm and unyielding as that of the strongest steel man-trap, and, 

 unless the assistance of a comrade, with a stout knife, or axe, or crowbar, is at hand, the victim 

 stands little or no chance of escaping a watery grave. Should such misadventure befall the 

 fisherman when wading, death approaches slowly with the rising ot the tide ; his fate in this 

 case being a less enviable one than if trapped by the bivalve when diving, under which circum- 

 stances drowning ensues speedily. Several instances of loss of life among the native Beche-de- 



