454 



EULAMELLIBRANCHIATA VENERACEA 



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, Urvilia. 



Fam. 7. Mdctridae. — External Ijranchial fold directed A'en- 

 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 

 A^alve, fitting into a branching tooth in the right valve, laterals 



present. Jurassic . Genera : Mactra, HarvcUa, Eaeta, 



Eastonia, Hetcrocardia, Vangandla. 



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 

 seldom byssiferous ; shell solid, equi^ilve, hinge usually with three 



cardinal teeth, laterals variable. 



Jurassic . Principal genera: 



Cytherea, Circe ; Grateloujoia (Ter- 

 tiary), Meroc, Dosinia ( = Artemis), 

 Cyirriiacria, Cyclina, Venus, Clem- 

 entia, ZucinojJsis ; Thetis (Creta- 

 ceous), Ta2?es, Venerupis. 



Fam. 2. Petricolidae.- — -Animal 



Fig. 307. — Ci/thei-ca dione'Li\,m.,'Ptxw. c i.- i in ^ 



■^ perforating rocks ; shell oval, 



slightly gaping l:)ehind, two or three cardinals, no laterals, 



pallial sinus well marked. Eecent . Genera : Petricola, 



jSfaranio. 



Fa^nl 3. Glaucomyidae. — Siphons long, united, foot small ; 

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

 pallial sinus well marked. Eecent. Genus, Glaucomya (inch 

 Tanysi])lioii). 



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 varial)le. 



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



