CLASS I PELECYPODA 473 



Opis Dcfr. (Fig. 758). Ti-igoiial, cordate, sinootli or concentrically striate ; Ijeaks 



Fio. 757. 



Astartc (GoodalUa) 

 miliaris Defr. Eocene ; 

 Grignon, • near Paris 

 (after Desliayes). 



Fig. 755. 



Astartc obliqua Desh. Interior 

 Oolite ; Bayeux, Calvados. 



Fig. 750. 



Digitari profunda De.sh. 

 (as Woodia). Eocene ; Aizy, 

 near Laon. A, Hinge, en- 

 larged. 75, Shell. 



prominent, prosocoelous ,; lunnle very deep, bordered by a keel; 

 cardinal teeth long, narrow (2 : 1). Trias to Cretaceous. 



Opisoma Stol. Jura. Seebachia Neuniayr. Cretaceous. 



Fig. 758. 



Opis goldfuasiana 

 d'Orb. Upper Jura ; Nat- 

 theim. Wiirtemberg. 



m 



Family 5. Crassatellitidae Dall. 



Shell as in the Astartidae, hut the valves always somewhat unequal, and usually 

 ore or less rostrate, the beaks compressed, erect or opisthocoelous ; Ivjament infernal, 



Fig. 75P. 

 Crassatellites i^lumhca (Chem.). Eocene (Calcaire Grossier) ; Damery, near Bpernay. 2/^. 



more or less obsolete, resilium large, wholly internal, attached at each end to a chondro- 

 phoric pit in the hinge plate behind the cardinal teeth ; lateral teeth and sockets usually 

 alternated in the valves, the hinge plate heavy, flat ; the posterior cardinal in the right 

 valve very small or obsolete, ivith no distinct socket in the opposite valve ; f^dl cardinal 

 , , L 1010 



Lower Cretaceous to Recent. 



Tlie earlier forms of this family have a small resilium close to the nearly marginal liga- 

 ment. With time, later ones show a gradual descent of tliese organs, until in some of tlie 

 more specialised modern representatives there is no ajtpreciable ligament remaining, and the 



