Lamarck's Genera of Shells. 31 



which it is suspended, however large and heavy it may be. The 

 cardinal teeth are on the anterior side, below the corselet. In 

 most species, the margin of the lunular aperture is crenate. 

 Type. Tridacna gigas *. (Chama gigas ? Linn.) 



Shell very large, transversely ovate ; ribs large, imbricate- 

 squamose; squamae short, arched, crowded ; interstices between 

 the ribs not striated. 



Indian Ocean, 7 Species. PI. I. Fig. 76. 



A shell of this species was given to Francis I. of France, by 

 the Republic of Venice, the valves of which are used to hold the 

 holy water, in the Church of Saint Sulpice, at Paris, Although 

 enormously large, there are others still larger. The biggest 

 known is said to weigh five hundred pounds. 



2. Hippopus f. 



Shell equivalve, regular, inequilateral, transverse; lunula 

 close. Hinge with two compressed, unequal, anterior, entering 

 teeth. Ligament marginal, external. 



The hippopus differs from the Tridacna, by having the lunula 

 shut; the margin of the valves at that part being indented, but 

 close together ; wherefore the animal cannot fix itself to rocks 

 by a byssus, like the tridacna, and consequently must have a 

 different organization from that of the preceding genus. 



The general form and appearance of the two shells is very 

 similar. 



One species. Hippopus niaculatus X, (Chama hippopus. Zmn.) 

 Shell transversely ovate, ventricose, ribbed, subsquamose, 

 white with purple spots ; lunula cordate, oblique. 

 Indian Ocean. PI. I. Fig. 77. 



2nd. Family. 

 Mytilacea, (3 Genera.) 

 Cardinal ligament subinternal, marginal, linear, very entire, 

 occupying a large portion of the anterior margin, and, by its 

 elasticity, tending to keep the valves open. 



The shell of the mytilacea is elongated, equivalve, regular, 



• Giant. f From iTrfro; a /locsc, and ir«; a. /ooi. i Spotted. 



