( 19 ) 



DIVISION XIII. TRIDACNEiE. 



GENERA. 



4. Tridacna. Brug. M. 



Shell regular, equival- 2 compressed cardinal 

 ved, inequilateral, gaping, teeth, unequal, anterior, 

 upper edge always undu- 

 lated ; with a byssus. 

 Fig. 51. 



2. Hippopus. Lam. M. 



Equivalved, regular, in- 2 compressed, une- Ligament marginal, 

 equilateral. Fig. 49. qual, cardinal teeth. exterior. (2) 



Ligament marginal, 

 exterior : muscular im- 

 pression elongated, at- 

 tached. (1) 



(1) These shells sometimes attain an enormous size, and are the largest and 

 heaviest known. Those which contain the holy water in the Church of St. Sulpice, 

 at Paris, were presented to Francis the First, by the Republic of Venice. The 

 tendinous byssus, which suspends them to the rock, is so thick and tenacious, 

 that it is only to be separated by a hatchet ; the flesh of the animal is eatable, 

 but very hard. Foss. Normandy, in the environs of Dives, . 



(2) There is but one species known. 



R 2 



