i 88 ] 
Australian Barrier Reef and on many places in the IndoMaJayan 
region. On Cocos Keeling Island it is so common that it is 
used as a washing tub. The largest specimen in the Museum 
measures 3 feet 6 inches in length. Its right valve weighs 191 
catties, its left valve 188 catties, giving a total of 505 lbs. 
(=229 kilos). Pelseneer makes the remarkable statement 
that these large Molluscs live only about eight years. If so, they 
would have to deposit carbonate of lime at the rate of 2'M oz. 
per day, in order to from those huge shells, an enormous 
amount, considering that these creatures live on microscopic 
animals only. However, it is perhaps not more remarkable 
than that the whale, the largest of all animals, living or extinct, 
derives its food from Copepods, minute Crustaceans, which are 
not much more than microscopic. The Clams have only one 
adductor muscle. Its impression, placed near the centre of 
each valve, is plainly visible in the exhibited specimen, 
being about 4 inches in diameter. Tridacna squamosa is 
a smaller species, with rows of pocket like scales on its 
surface. Allied to the Clams is Hippopus macukiiits. , Its 
generic name signifying * Horse's foot ' is due to the re- 
semblance which its two valves when placed together, have 
to a horse's hoof. The Razor-shell {Sale») has its popular 
name from its long straight valves, resembling the handle of a 
razor. It burrows in sand and can do so with great rapidity, 
escaping even capture. Very remarkable through their habits 
are the boring shells. Pholas bores in hard clay and chalk, or 
even limestone and sandstone. Xyiophaga (literally the ' Woo<l- 
eater ') and Teredo (i.e. the ' Borer ') bore in wood. Teredo, the 
Ship-Worm, is well-known through the ravages which it does to 
the timber of ships and harbour works. Its shell is only small, 
about %. inch in size. Its siphons, however, are enormous, 
reaching two or three feet in length, and on account of its in- 
conspicuous shell the older naturalists, ilicluding even Linnaeus, 
took it for a worm. It lines the tunnels which it excavates, 
with a calcareous tube. Aspergillum { = Brechites), the last 
species we have to mention, is in shape perhaps the most 
remarkable of all Lamellibranchs. It has a pair of normal 
valves only when quite young. But its long siphons soon 
secrete a tube which is open at the one end, and closed at the 
other by a sieve-like perforated disk. The original valves, only 
about ?^ inch in length, become soldered into this tube. This 
mollusc lives buried into the sand, with the sieve-like end 
projecting. 
