MOLLUSCA. 
291 
This paper is full of important information. In the intro- 
duction the history of our knowledge of this family is given ; 
a species of Tridacna seems to be alluded to by Pliny in a very 
indistinct manner^ and the name mentioned by him was first 
given to these shells by Belon. Tridacna elongata (Lam.) has 
been observed alive at Suez by the author ; it is buried in the 
sand, with the lunula downwards, the scalloped ventral edges 
only being visible; the larger individuals are said to be found at 
greater depths. The gaping of the valves is continuous during 
life, as long as the animal is not disturbed, as individuals may 
be found in which a pathological incrustation of evidently slow 
growth renders the shutting of the valves impossible ; the valves 
gape comparatively wider , than in other bivalves, the author 
halving measured a gaping of centimetres (about an inch) in 
a living individual 12^ centimetres long. They are eaten by 
the natives, and the shells burnt to lime. The animals render 
spirits of wine of a very beautiful reddish violet colour. 
In the descriptions the terms above and below, in front and 
behind, are used as in other shells, the vertices being termed 
above and the lunula in front, although the real situation of 
the living animal would warrant a different terminology. The 
mantle reaches beyond the edges of the shell,- and has three 
openings — one at the lunula for the foot, the second quite in 
front for admitting water to the gills, and the third about in 
the middle of the length of the ventral edge of the valves for 
the ejection of water and excrements. All these openings are 
situated more towards ’ the front than in other bivalves, with 
regard to the regions of the shell, but when the real situation of 
the whole animal during life is taken into consideration, the 
position of the openings is similar to that generally found in 
this class. The portion of the mantle within the pallial line, 
which adheres closely to the shell ; does not contain distinct 
contractile elements ; but the portion beyond it is very muscular, 
and contains also large arteries. The space enclosed by the 
mantle is only half filled by the visceral organs of the body, the 
other half being occupied by water entering from the outside. 
The mouth is situated in front and above ; the intestine tra- 
verses the heart; the gills are lamellated and contain the fry; 
as in other bivalves ; in all the individuals examined the little 
pseudoparasitical crab, Pinnoteres tridacn(R (Riippell), was found 
near the gills. 
The shell resembles in its microscopical structure most that 
of Chama, being rather indistinctly prismatic and traversed by 
anastomosing, not very numerous channels. The arrangement 
of the muscles is that of the other Monomyaria which are pro- 
vided with a foot, — the principal being the single large adductor 
of the valves, a retractor, and a protractor of the foot — the two 
latter being double, one on each side. As the retractores are 
u 2 
