i BIVALVE MOLLUSCA. 347 
vf 
when at a little depth beneath the surface a number of these animals 
display the brilliant velvety “colours and varying shades of their 
submarine parterres. As we can only perceive the gaping opening of 
_:thé valves, we may imagine to ourselves what is its entire aspect.” 
sag The mantle of the animal is closed and ample ; its edges are swollen, 
and reunited in nearly its whole circumference in such a manner as 
to leave only three very 
small openings—two in the 
upper part; the one serves 
the purpose of discharging 
the products of digestion, 
the other gives entrance 
and exit to the water ne- 
cessary for respiratory pur- 
poses. The third opening 
is in the lower part of the 
body, and free ; it leaves an 
opening for the passage of 
the foot, which is enormous, 
and is surrounded with an 
ample tuft of byssoidal 
fibres. 
Aided by this silky tuft, 
the animal attaches itself to 
the rocks, and suspends its 
weighty shell from them. 
If it is intended to remove 
those attached to the sides 
of the rock, it is necessary 
to cut the cords of the ten- 
donous byssus by which it 
is held suspended with a 
hatchet. Fig. 149.—Tridacna squamosa, on the inside (Lamarck) 
All the species are in- 
habitants of the tropicai seas. The Zridacna gigas is a native ot 
the Indian Ocean. The flesh, though leathery and by no means ot 
an agreeable flavour, is a great resource to the poor Indians. The 
accompanying representations of Ziidana squamosa (Figs. 148 and 
149) will convey a general idea of the genus. 
The fourteenth family, Hippuritidz, is entirely fossil; but the 
fifteenth, Chamidee, of which the best example is the typical genus 
Chama, is widely distributed in tropical seas. 
