206 
CXXXI. Acardo. A shell formed of two flattened and nearly 
equal valves, having neither hinge nor cartilage, but a muscular im- 
pression in the middle of the valves. 
This genus, which has been adopted by Bruguiere and Lamarck, was 
formed by M. C-ommercon, from a shell he discovered during his voy- 
age round the world. The shell seen by M. Commercon was somewhat 
cordiform, and its substance appeared to be intermediate between shell 
and bone. Being attached to the centre of the two valves, the animal 
was able thereby to separate the valves, and in a parallel direction. 
Bruguiere reported that he had seen a shell of this genus in the Isle of 
France, the shape of which was nearly square. No fossil shell of this 
genus is known. Hist. Nat. des Coq. par Bose. T. n. p. 325. 
CXXXII. Radiolites. An irregular inequivalved shell, striated 
outwardly. The inferior valve in the form of a reversed cone : the 
superior convex. Neither hinge nor cartilage. 
These fossils agree with the shells of the preceding genus in the 
absence of hinge and cartilage, but differ essentially in their figure. 
Bruguiere had united them in one genus, but Lamarck made the war- 
rantable separation. These fossils were first noticed by M. Picot de 
la Peyrouse, Description d’ Orthoceratites, Sfc. who considered them 
as a particular species of oysters. Plate XVI. Fig. 1, represents one 
of these fossils, as engraved in the work of Picot, Tab. 12, Fig. 4. 
These fossils were obtained from that part of the Pyrenees which is 
named Les Corbieres, and chiefly from that part which extends from 
Monferrand to Sougragne. 
CXXXIII. Chama. An inequivalved, adhering bivalve, with un- 
equal incurvated beaks. The hinge with one thick, oblique, and 
sometimes crenated tooth. Two muscular impressions. 
Bruguiere, properly limiting this genus to those snells possessing 
one hinge-tooth ; those shells in whose hinge were two or three teeth, 
and which used to be placed under this genus, are now disposed 
under Cardita, Tridacna, Hippopus, and Isocardia. 
The fossil chama; of the neighbourhood of Paris appear to correspond 
