197 



cular, and flattish, and furnished, on its inner surface, with 

 two unequal, subconical, curved tuberosities ; the lower 

 valve larger, rather subventricose, with squamae radiating 

 beyond its border ; the .cavity is obliquely conical, having, 

 on one side, a keel or ridge, as if formed by a fold of the 

 inner surface, which is transversely striated; the hinge is 

 unknown. Fossil. 



There is only one species known. From the Isle of Aix. 



2. Radiolites. An unequal valved bivalve, striated ex- 

 ternally with longitudinal rays ; the lower valve, which is 

 the larger, is turbinated ; the superior is convex or conical, 

 like an operculum ; the hinge is unknown. Fossil. PL vi. 

 fig. 22. 



3. Calceola. An unequal valved, triangular, subturbi- 

 nated bivalve, flat beneath ; the large valve like a hood, ob- 

 liquely truncated at its opening ; the hinge margin straight 

 and transverse, being slightly notched and dentated in its 

 middle ; the upper margin bowed ; the less valve flat, semi- 

 orbicular, like an operculum, with two lateral tubercles on 

 its hinge-margin, and, in its centre, a small pit. Fossil. 

 PL viii. fig. 24. 



4. Acardo. A flat, nearly equivalved bivalve, having 

 neither hinge nor ligament, with one impression in the 

 centre of the valves. Recent. PL vi. fig. 21. 



This shell is admitted, by Lamarck, in La Systeme de 

 la Nature, but is not mentioned in his Histoire Naturelle 

 des Animaux sans Vertebres. 



5. Birostrites. An unequal bicornuted bivalve; the 

 disks of the valves raised into unequal, rather straight, ob- 

 liquely divaricating cones, resembling horns, the base of the 

 shortest being surrounded by that of the other. 



Found only as a fossil. Its locality does not appear to 

 be known. 



6. Distinct. An unequal valved, ovate, roundish bivalve, 

 a little depressed ; the valves equal in size, with a very dis- 



