XVI EULAMELLIBRANCHIATA— SUBMYTILACEA 45 1 



Order IV. Eulamellibranchiata 



Mantle edges united at one or more points, branchiae with in- 

 terfilamentary junctions which are always vascular, genital glands 

 not opening into the kidneys, usually two adductor muscles. 



Sub-order I. Submytilacea. — Mantle edges more or less 

 open, anal orifice distinct, usually no siphons, pallial line usually 

 simple, cardinal and lateral teeth well marked. 



Fam. 1. Carditidae. — Foot with a byssus or groove, branchiae 

 large, unequal ; shell equivalve, solid, radiately grooved, one or 



two oblique cardinal teeth, one or two laterals. Silurian . 



Principal genera : Venericardia, Cardita, Carditella^ Carditopsis, 

 Milneria ; Pleurophorus (Palaeozoic), Anodontopsis (Silurian). 



Fam. 2. Astartidae. — A short anal siphon, labial palps large ; 

 shell triangular, thick, ligament external, hinge with two or 



three cardinals in each valve, laterals obscure. ? Devonian . 



Principal genera: Astarte; Pachytypiis (^J nrsissic') ^ Plesiastarte 

 (Eocene), Pai^astarte, Woodia^ Opis (Secondary strata), Proso- 

 coelus (Devonian). 



Fam. 3. Crassatellidae. — Mantle with anal orifice or open; 

 shell equivalve, thick, subtriangular, ligament in an internal 

 fossette, hinge with two cardinals, laterals produced. Creta- 

 ceous . Principal genus, Crassatella. 



Fam. 4. Cardiiiiidae. — Shell equivalve, oval or triangular, 

 ligament external, cardinal teeth small, laterals fairly strong. 



Devonian Oolite. Principal genera : Cardinia^ Anthraeosia, 



Carhonicola^ Anoplophora. 



Fam. 5. Cyprinidae. — Anal and branchial orifices complete, 

 papillose, foot thick ; shell variable, equivalve, 

 thick, umbones often spiral, hinge-teeth very 



variable, ligament external. Jurassic . 



Principal genera : Cyprina ; Pygocardia 

 (Crag), Veniella (Cretaceous), Venilicardia 

 (Secondary strata), Anisocardia (Jurassic), 

 Isocardia, Llhitina^ Coralliophaga; Basterotia 

 (Eocene). The families Pachydomidae (Pa- 

 laeozoic) and Megalodontidae (Palaeozoic — ^iQ.m^.—lsocardiavul- 

 Secondary) are probably related to the Cyp- gans Reeve, China. 

 rinidae. 



Fam. 6. Aetheriidae. — Anal orifice complete, foot absent, 



