Lamarck's Genei'a of Shells. 47 



The rudista are allied to the ostracea in certain respects, but 

 are eminently distinguished from them, by having neither hinge, 

 valvular ligament, nor muscle of attachment, nor any indication 

 of the places where these objects should be found. As they 

 are all fossil-shells, we can form no idea of the characters of 

 the animal that once inhabited them. 



1 . Sphoerulites *. 



Shell inequivalve, orbiculo-globular, somewhat depressed 

 above, externally echinate with large, subangular, horizontal 

 scales. Upper valve smallest, rather flat, opercular : its in- 

 ternal surface furnished with two unequal, subconical, curved, 

 and projecting tuberosities ; lower valve larger, rather ventricose, 

 with radiating scales, extending beyond the margin; cavity ob- 

 liquely conical, forming on one side, by the folding of the inter- 

 nal margin, a crest, or projecting keel. Interior of the cavity 

 transversely striated. Hinge unknown. 



The sphoerulites differ from the radiolites by having large 

 subangular scales on their exterior surface, which gives them a 

 foliated appearance, and by some dissimilarity in point of form, 

 their upper valve being rather flattened, instead of conical ; and 

 it seems doubtful, if the interior surface of the smaller valve of 

 the radiolites have the two tuberosities of the sphoerulites ; or 

 if the crest, or projecting keel, formed by the folding of the in- 

 ternal margin, on one side of the cavity, can be found in its 

 greater valve. 



One Species. SphceruUtes foliacea t. 

 No further description. Isle of Aix. PI. II, Fig. 98. 



2. Radiolites i. 



Shell inequivalve, externally striated; striae longitudinal, ra- 

 diating. Lower valve turbinated, largest; upper valve convex, 

 or conical, opercular. Kinge unknown. 



The radiolites appear to be formed of two, often very unequal 

 cones, applied base to base, and externally striated, but are not 

 squamose. These fossils are only found in the older formations; 

 they are tolerably abundant in the Pyrenees. 



• From sphetrula, it little fflolu: t Foliaceous. I From radius, a ray. 



