340 



THE OCEAN WORLD. 



giga* is a native of the Indian Ocean. The flesh, though coriaceous, 

 and by no means of an agreeable flavour, is a great resource to the 

 poor Indians. The accompanying representations of Tridacna squa- 

 mosa (Figs. 149 and 150) will convey a general idea of the genus. 



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

 fifteenth, Chamidae, of which the best example is the rugose genus 

 Charina, is widely distributed in tropical seas. 



The very numerous division of shells called Asiphonidae, possesses 

 animals without respiratory siphons. The shells we shall now describe 

 belong to the sixteenth family, Unionidae, which contain Iridina, 

 Anodon, and Unio. 



The pond mussels, Anodon, are found in lakes, rivers, and seas of 

 almost every region of the globe. Their shells are rounded or oval, 

 generally very thin, regular, and equivalve, not gaping, the hinges 

 without teeth, whence their name, from the Greek, oS<Wo?, without 

 teeth. These shells are nacred inside, and generally smooth. 



The Anodon cygnea (Fig. III., PL. XYI.) is broad, deep, and light, 

 and is sometimes employed for skimming the cream off milk. The 

 genus is divided into many groups, the principal forms of which are 

 represented in PL. XYI. 



The river mussels, Unio, are, like the Anodon, found in the muddy 



bottoms of all countries. 

 The animal resembles the 

 Anodon, but the shell pre- 

 sents a toothed hinge. 

 The lower face of the valve 

 is nacrous, but shaded with 

 purplish violet, copreous, 

 and iridescent; the an- 

 terior face is of a green 

 colour, which varies from 

 tender to blackish green. 



Among the species found 

 in European seas may be 

 noted the Ehine mussel, 

 Fig. i5i. umo nttoraiis (Cuvier). a J ar g e species, the nacre 



of which is employed for ornamental purposes. Unio littoralis 

 (Cuvier), represented in Fig. 151, and the painter's mussel, Unio 



