C R A IN I A Parisiensis. 
TAB. CCCCVIII. 
SJfec. 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. — JLamarck Hist . Nat. VI* 
pt . 1,259. Cuvier and Brogniart Geo L des. 
■env. de Paris , ed. 1822, p. 15, /. 3, f. 2. 
G. B. Sowerby Genera, plate of Cranice, fig . 3. 
JThe upper valve is smooth in the centre; its umbo is 
small, pointed, and a little Accent ric ; 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 com- 
posed of spheerical 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 impressions 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 age, although not confined t© 
