( n ) 



DIVISION XVIII. RUDISTES. 



Hinge unknown. (1) 



Hinge unknown. (2) 



GENERA. 



1. SpHjErulites. Lam. 



Foss. 



Shell inequivalved, or- 

 bicularly globulous, a lit- 

 tle depressed above, armed 

 exteriorly with large sub- 

 angular horizontal scales : 

 upper valve smaller, flat, 

 like an operculum, with 

 two unequal sub-conical 

 tuberosities (curved and 

 projecting) within; infe- 

 rior valve larger, a little 

 swelled ; radiating scales 

 outside the edge forming 

 a crest or projecting keel 

 by a fold of the inner 

 edge. Fig. 93. 



2. Radiolites.Z,#/?z. Foss. 



Inequivalved, striated • 

 exteriorly, stria? longitu- 

 dinal, radiating : lower 

 valve turbinated, largest ; 

 upper valve convex, or 

 conical, like an opercu- 

 lum. Fig. 92. 



3. Calceola. Lam: Foss. 



(3) 



Inequivalved, triangu- 

 lar, turbinated, flattened 

 underneath : the large 

 valve hollowed like a 

 hood, obliquely truncated 

 at the opening, with its 

 cardinal edge straight, 

 transversal, a little sloped 

 and sub-dentated in the 

 middle , and its upper edge 

 arched ; the small valve 

 flattened, semi-orbicular, 

 in the form of a lid, 

 having a tubercle on each 

 side of its cardinal edge, 

 and, in the middle, a 

 hollow with a small scale. 

 Fig. 94. 



(1) There is but one species known, from the Isle of Aix. 



(2) These shells are only found in beds of antient formation ; the Pyrenees con 

 tain a considerable number. They are the same as the Ostracites of La Peyrouse, 

 and the Acardlnes of Guvier. The Acardo of Bruguicre, adopted by Lamarck, is a 

 double epiphysis of the vertebra of a Cetacea, 



0) Ip the environs of Juliets, 



