MOLLUSCA. 
88 
Flacuna, Brug. 
A small genus allied to the Anomiae, in which the valves are thin, 
\mequal, and frequently irregular, as in the latter, hut both entire. 
Two projecting ribs, en chevron, are seen on the inside of one of 
them, near the hinge. 
The animal is not known, hut it must resemble that of the Ostreae, 
or that of the Anomiae * * * § . 
Spondylus^ Lin. 
A rough and foliaceous shell as in the Ostreae, and frequently spiny ; 
but the hinge is more complex ; besides the cavity for the ligament, 
analogous to that of the Ostreae, there are two teeth to each valve 
that enter into fossae in the opposite one; the two middle teeth be- 
long to the most convex valve, Avhich is usually the left one, and 
Avhich has a projecting heel, flattened as if salved through behind 
the hinge. The animal, like that of a Pecten, has the borders of its 
mantle furnished with two rows of tentacula, some of the external 
ones being terminated by coloured tubercles ; before the abdomen is 
a vestige of a foot formed like a broad radiated disk on a short pe- 
dicle, and endowed with the faculty of contraction and expansion f. 
From its centre hangs a filament, terminated by an oval mass, the use 
of which is unknown. 
"J’he Spondyli are eaten like oysters. Their shells are frequently 
tinged with the most brilliant colours. They adhere to all sorts of 
bodies;!;. 
Plicatula, Lam. 
The Plicatulae, separated by Lamarck from the Spondyli, have 
nearly the same kind of hinge but no heel, and flat, almost equal, irre- 
gular, plicated and scaly valves, as in many of the Ostreae §. 
Malleus, Lam. 
A simple pit for the ligament as in the Ostreae, where the Mallei were 
left by Linnaeus, on account of their having the same irregular and 
inequivalve shell, but distinguished by a notch on the side of this liga- 
ment for the passage of a byssus. 
The most known species, Osirea malleus, L.; Chemn., VIII, 
Ixx, 655, 656, which ranks among the number of high-priced 
and rare shells, has the two ends of the hinge extended and 
forming something like the head of a hammer, of which the 
valves, elongated in a transverse direction, represent the handle. 
It inhabits the Archipelago of India. 
There are some others, possibly young ones of the same species, in 
* Anomia placenta, Chtran., VIII, Ixxix, 716; — An. sella, Ib., 714. See also 
pi. 173 and 174 , Encyc. Method., Vers. 
'b Called by Poll “ the abdominal trachea" in the Spondyli, &c. 
t Spondylus geederopus, Chemn., VII, xliv, et seq., IX, cxv ; — Sp. regius. Id., xlvi, 
471. 
§ Spond. plicatus, L., Chemn. VII, xlvii, 479, 4S2 ; — Plicat. cegyptia, Savign., 
Egyp. Coq. pi. xiv, f. 5. 
