BIVALVE MOLLUSCA. 



347 



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 

 the valves, we may imagine to ourselves what is its entire aspect" 

 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 Fig. 148.— Tridacna squamoba (Lamarck). 



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. 



All the species are in- 

 habitants of the tropical seas. The Tridacna gigas is a native ol 

 the Indian Ocean. The flesh, though leathery and by no means of 

 an agreeable flavour, is a great resource to the poor Indians. The 

 accompanying representations of Tridacna squamosa (Figs. 148 and 

 149) will convey a general idea of the genus. 



The fourteenth family, Hippuritidae, is entirely fossil ; but the 

 fifteenth, Chamidae, of which the best example is the tj'^pical genus 

 Chama, is widely distributed in tropical seas. 



Fi^. 149. — Tridacna squamosa, on the inside (Lamarcfe) 



