454 



EULAMELLIBRANCHIATA — VENERACEA 



CHAP. 



Fam. 5. Cardiliidae. — 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 fossette, 

 another portion external, a bifurcated cardinal tooth in the left 

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



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



Eastonia^ Ifeterocardia^ Yanganella. 



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 : 



Cytlierea^ Circe; Grrateloupia (Tev- 

 tmvy')^ Meroe^ Dosiiiia (^ = Artemis)^ 

 Cy primer ia^ Cyclina^ Venus, Clem- 

 entia, Lucinopsis ; Thetis (Creta- 

 ceous), Tapes, Venerupis. 



Fam. 2. Petricolidae. — Animal 

 perforating rocks ; shell oval, 

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



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



Fam. 3. Glaucomyidae. — Siphons long, united, foot small; 

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



pallial sinus well marked. Recent . Genus, G-laucomya 



(inch 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. Cardiidae. — Siphons rather long, foot long, no 

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



Fig. 307. — Cytlierea cllone Lam., Peru. 



