ACEPHALA TESTACEA. 393 



the valves of which do not even appear to have been held to- 

 gether by a ligament, but which covered each other like a vase 

 and its cover, and were connected by muscles only. They form 

 the genus 



AcARDA, Brug. — OsTRAciTA, La Peyr., 



Of which M. de Lamarck makes a family that he names Rudista. 

 The shells are thick, and of a solid or porous tissue. They are now 

 divided into the 



Radiolites, Lam., 



In which the valves arc striated from the centre to the circumfe- 

 rence. The one is flat, the other thick, nearly conical and fixed(l). 



Sph^rulites, Lameth., 



Where the valves are roughened by irregularly raised plates. It 

 is also thought we may add the 



Calceola, 



One valve of which is conical but free, and the other flat and even 

 somewhat concave, so that they remind us of a shoej and even the 



HiPPURITES, 



Where one valve is conical or cylindrical with two obtuse, longi- 

 tudinal ridges on the inside; the base even appears to be divided into 

 several cells by transverse septa(2)j the other valve fits like a cover. 

 The 



Batolithes, Montf. 334, 

 Are cylindrical and straight Hippurites; they are frequently found 



(1) The species of Brugiere, 173, f. 1, 23, which forms the genus Acahda, Lam., 

 appears to be nothing more than a double epiphysis of the vertebra of some ceta- 

 ceous animal. The Discin/^, Lam., are Orbiculae; it is also thought that his 

 Craniae should be approximated to them. The Jodamies of M. de France or 

 BiRosTEiTEs, Lam., are mere moulds of Sphcehulites or at least of tlie bodies 

 always found in their interior, although they do not adapt themselves to their form. 

 See M. Charles Desmoulins on the Spherulites. 



(2) See Deshayes, Ann. des Sc. Nat., June, 1825; and Ch. Desmoulins, loc. cit. 

 Several Hippurites have been described by La Peyrouse under the improper 

 name of Orthoceratites. The Cornucopix of Thompson, Journ. de Phys. an. X, pi. 

 ii, is also one of them. 



Vol. II.— 2 Z 



