HIPPOPUS. 



Hist. Nat. des Aiiim. sans vert. 



TESTA aequivalvis, regularis, in£eqiiilatera5 sub- 

 transversa vel loiigitiidinalis, lunula clausa, 

 margine siniioso. Cardo dentibus cluobiis com- 

 pressis, elongatis, ina3qualibus5 anticis, in valva 

 altera ; tribus, quorum unus obsoletiuseulus in 

 altera. Ligaraentimi marginale, externum. 



The HlppojMS mavulatus of Lam. Chcima Hlppopiis oi Linn* 

 lias long* been deservedly esteemed by collectors; when 

 fine it is certainly a very ornamental shell. Lamarck has 

 separated it as a Genus from his Tridacna; on accomit of 

 the edges of the two valves nearly meeting all around ; 

 while in Tridacna there is a large opening, for the passage 

 of tendinous fibres by which it adheres to the rocks. 

 Whether the Hippopus also attaches itself in the same 

 manner to the rocks or not we have not the means of 

 ascertaining; Lamarck seems to think it does not, because 

 the lunule is closed, but we know several genera which 

 do attach themselves to the rocks, stones, &c. by a byssus 

 and yet have not so much space left between the valves 

 for its passage as this has. 



Shell equivalve, inequilateral, regular, subtransverse 

 or longitudinal, the greater part of the margin more or 

 less deeply sinuous, and not gaping behind. All that we 

 have ever seen are covered on the outside by larger or 

 smaller radiating costae, which are frequently crossed at 

 various intervals by irregular rows of small, sometimes 



