CLASS I 



PELECYPODA 



471 



This family, so well known under the i)reoccupied name Cyprinidae, probably shared the 

 same origin as the Astartidae, and tlie two do not definitely separate until the Jura. The 

 position of the Paleozoic ancestors is necessarily doubtful, and they are placed ditferently 

 by different authors. The group is divided into two subfamilies, Plcurophorinae and 



Veniellinae. 



PleuropJiorus King (Fig. 749). Elongated, sul)-rectangnlar ; beaks sub-terminal ; 

 surface smooth or with radial sculjiture ; hinge with two cardinal teeth in each valve ; 



Fui. 749. 



Pleiirophonis eostatus King. Per- 

 mian ; layers Quarry, England. A, 

 Shell, Vi (iifter King). B, Internal 

 monld Ironi Gera, Thnringia (after 

 Geinitz). 



Fiii. 750. 



Anisoc/irdia elegans Mun.-Chalm. Kimmeridgian ; 

 Cap de la Heve, near Havre, i/i- 



anterior adductor scars deep, with a buttress-like ridge liehind it. Devonian to 

 Trias ; esiiecially abundt'int in the Permian. 



Gypricardella Hall [Microdon Hall); Mecynodon Keferst. ; Gypricardinia Hall. 

 Devonian. Astartella Hall. Carboniferous. 



Anisocardia Mun.-Chalm. (Fig. 750). 



Rounded or trapezoid, plump, smooth or 

 radially striate ; posterior slope some- 

 times keeled ; hinge with a strong 

 sometimes bifid right cardinal behind, 

 and an anteriorly directed front cardinal; 



Arctlca islandicit (Linn). Pleis- 

 tocene ; Boliusliin, Sweden. 



Venilicardia cordiformts, d'Orb. 

 Gault ; Seignelay, Yonne. 



Fic. 753. 

 Veniella tumida Nyst. Crag ; Antwerp. 



left valve with a forwardly directed anterior and a posterior cardinal tooth. Jura to 

 Tertiary. 



Roudairia Munier-Chalm. Like Trapeeium, but with a sharp keel and smooth 

 area behind, anteriorly with concentric ridges ; right posterior cardinal bifid. Upper 

 Cretaceous. 



