TRIDACNA. 



Lam., Hist. Nat. des Anim. sans vert. 



TESTA sequivalvis, regularis, insequilateralis, 

 lunula hiante, margine ventral! sinuoso ; cardo 

 alterius valvae, dentibus duobusposticis, quorum 

 alter brevis, alter elongatus; alterius, tribus, 

 quorum unus brevis, duo elongati. Ligdmentuni 

 submarginale, sub-externum, fulcro intra-mar- 

 ginali. Animal bysso tendineo rupibus affixum. 



Few genera are so perfectly distinct as the present ; sepa- 

 rated from all others by characters peculiar to itself, it 

 can scarcely even be said to be nearly related to any, if 

 indeed we except Hippopus, to which in general form and 

 in its remarkably sinuated edge it is closely allied. This, 

 together with Hippopus, Cardita, Chama and others of 

 very different characters are associated by Linneans under 

 the generic appellation of Chama, than which association 

 nothing can be less natural 



One species of this beautiful Genus is remarkable for 

 the enormous magnitude to which it attains, the T, Gigas ; 

 it is the most gigantic of all shells; we refer to Dillwyn 

 for an account of a pair of the valves of this species, 

 which are used as ^'Benitiers'' in the church of St. Sulpice, 

 at Paris, weighing more than 500 pounds, and Lamarck 

 speaks of even larger. 



Shell equivalve, regular, inequilateral, generally lon- 

 gitudinal, with a wide opening placed immediately anterior 

 to the umbones, for the passage of a strong tendinous 



