454 EULAMELLIBRANCHIATA — VENERACEA chap. 



Fam. 5. CardiUidae. — Shell heart-shaped, hinge as in 

 Mactridae, posterior adductor resting on a myophore or shelf. 



Single genus, Cardilia. Tertiary . 



Fam. 6. Mesodesmatidae. — Mantle edges largely united, 

 with three orifices, foot byssiferous or not; shell regular or 

 irregular, usually one cardinal and strong lateral teeth. 



Tertiary . Genera: Mesodesma^ Ervilia. 



Fam. 7. Mactridae. — External branchial fold directed ven- 

 trally, siphons fused, foot tongue-shaped ; shell equivalve, 

 triangular-oval, hinge with ligament in an internal fosse tte, 

 another portion external, a bifurcated cardinal tooth in the left 

 valve, fitting into a branching tooth in the right valve, laterals 



present. Jurassic . Genera : Nactra., Harvella^ Raeta^ 



Eastonia^ Heterocardia., Vanganella. 



Sub-order III. Veneracea. — Branchiae slightly folded, 

 foot compressed, siphons generally short, pallial line variable, 

 two adductor muscles. 



Fam. 1. Veneridae. — Siphons free or partly united, foot sel- 

 dom byssiferous ; shell solid, equivalve, hinge usually with three 



cardinal teeth, laterals variable. 



Jurassic . Principal genera : 



Cytherea^ Cii^ce ; Grrateloupia (Tqt- 

 tisiYy'),Meroe, I)osinia(^ = Artemis'), 

 Cyprimeria, Cyclina^ Venus, dem- 

 entia, Lucinopsis ; Thetis (Creta- 

 ceous), Tapes, Ve7ierupis. 

 ^ .,^^ ^ , Fam. 2. Petricolidae. — Animal 



Fig. 307. — (;?/f/ie?'eadione Lam., Peru. ... -, i m , 



periorating rocks ; shell oval, 

 slightly gaping behind, two or three cardinals, no laterals, pallial 

 sinus well marked. Recent . Genera: Petricola, Naranio. 



Fam. 3. G-laucomyidae. — Siphons long, united, foot small; 

 shell produced, thin, hinge with three cardinals, no laterals, 



pallial sinus well marked. Recent . Genus, Glaucomya 



(incl. Tanysiphori). 



Sub-order IV. Cardiacea. — Branchiae much folded back, 

 mantle edges with three apertures, foot cylindroidal, more or 

 less produced, siphons present or absent, one or two adductor 

 muscles, pallial line variable. 



Fam. 1. Oardiidae. — Siphons rather long, foot long, no 

 byssus ; shell equivalve, more or less radiately ribbed, hinge with 



