CONCHIli'ERA. 



447 



tlie deep and rugose cartilage pits : loiuer valve with a thick outer 

 layer, often foliaceous ; its cayity deep and straight, with two 



Fig, 241. Interior of lower valve. Fig. 242. Interior of tipper valve. 



JRadiolites mammillariSf Math. |. L, Chalk. S. Mamest, Dordogne. 



f', ligamental inilection; m, pallial Hne ; c, c, cartilage pits ; a, a, adductor impressionfi 



and processes ; t, teeth and'dental sockets. 



dental sockets and lateral muscular impressions; upper valve 

 flat or conical, with a central umbo ; outer layer thin, radiated ; 



Fig. 243. Side views of the upper valve of E. mammillaris ; I, hgamental inflection 3 

 t, teeth ; a, a', muscular processes. 



umhonal cayity inclined towards the, ligament ; teeth angular, 

 striated, supporting, curved and sub-equal muscular processes. 



The upper yalye of E. fleuriausus has an oblique umbo, with 

 a distinct ligamental groove. The* foliations of the lower valve 

 are frequently undulated ; they are sometimes as thin as paper, 

 and several inches wide. 



The umbonal cayity of the lower valve is partitioned off by 

 very delicate fannel-shaped laminae. Specimens frequently 

 occur in which the outer shell layer is preserved, whilst the 

 inner is wanting, and the mould ("birostrites") remains loose 

 \i the centre. The interior of the outer shell layer is deeply 



