206 



CXXXI. Acardo. A shell formed of two flattened and nearly equal 

 valves, having neither hinge nor cartilage, but a muscular impression in 

 the middle of the valves. 



This genus, which has been adopted by Bruguiere and Lamarck, was 

 formed by M. Commercon, from a shell he discovered during his voyage 

 round the world. The shell seen by M. Commercon was somewhat cor- 

 difbrm, 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. Bru- 

 guiere 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 Bosc. T. n. p. 325. 



CXXXII. Radiolites. An irregular inequivalved shell, striated out- 

 wardly. 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 arid cartilage, but differ essentially in their figure. Bruguiere 

 had united them in one genus, but Lamarck made the warrantable sepa- 

 ration. These fossils were first noticed by M. Picot de la Peyrouse, 

 Description d'Orthoceratites, fc. who considered them as a particular spe- 

 cies of 'oyters. Plate XVI. Fig. I, represents one of these fossils, as 

 engraved in the work of Picot, Tab. 12, /. 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. Ckama. An icequivalved, adhering bivalve, with unequal 

 incurvated beaks. The hinge with one thick, oblique, and sometimes 

 crenated tooth. Two muscular impressions. 



Bruguiere, properly limiting this genus to those shells 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 Car- 

 dita, Tridacna, Hippopus, and Isocardia. 



The fossil chamae of the neighbourhood of Paris appear to correspond 



