CRAINIA Paiisiensis. 

 TAB. CCCCVIII. 



Spec. Char. Suborbicular, depressed ; upper 

 valve thin, obscurely granulato-spinose, 

 smooth in the centre; lower valve thick, 

 with the margin much elevated, and of a 

 conspicuously cellular structure. 



Syn. Crania Parisiensis, De France Diet, des 

 Sciences natur. — Lamarck Hist. Nat. VI, 

 pt. I, 259. Cuvier and JBrogniart GeoL des. 

 env. de Paris, ed. 1822, p. 15, /. 3, /. 2. 

 O. B. Sower hi/ Genera, plate of Crania, fig. 3. 



J. HE upper valve is smooth in the centre ; its umbo is 

 small, pointed, and a little eccentric ; the margin de- 

 scends over the elevated edge of the lower valve, is* 

 covered with short, depressed, scattered spines, and is 

 rather rugged ; the lower valve has a few obscure, di- 

 verging striae upon its inner surface, it is attached by 

 the whole of its outer surface, except what is covered by 

 the margin of the other valve ; a great part of it is cona- 

 posed of sphaerical cells, which are most conspicuous 

 around the margin when uncovered, by the removal of 

 the upper valve ; the muscular impressions are very 

 variable, sometimes they are hardly to be traced, at 

 others they are very deep ; the elevation between the 

 central ones also varies, sometimes it is very prominent 

 with the imj>ressions raised along with it : when the im- 

 pressions and elevation are distinctly marked, the general 

 resemblance to the front of a human skull is very strong ; 

 (hence the generic name). The depth of the impressions 

 seems to be the result of ago, although not confined to 



