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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. — PI. 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. 

 —PI. 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. — PI. 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. Discina. — An unequal valved, ovate, roundish bivalve^ 

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



