EULAMELLIBRANCHIATA SUBMYTILACEA 



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Order IV. Eulamellibranchiata 



Mantle edges united at one or more points, branchiae with 

 interfilamentary junctions wliich 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 oritice distinct, usually no siplions, pallial line usually simple, 

 cardinal and lateral teeth well marked. 



Fam. 1. Cktrditidae. — 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, CardAta, Carditella, Cardito'psis, 

 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 ; Pachytyjous (Jurassic), Plesiastarte 

 (Eocene), Parastarte, Woodia, Ojjis (Secondary strata), Prosocoelv.s 

 (Devonian). 



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

 shell equivalve, thick, subtriangular, ligament in an internal fos- 



sette, hinge with two cardinals, laterals produced. Cretaceous . 



Principal genus, Crassatella. 



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

 ligament external, cardinal teeth small, laterals fairly strong. 



Devonian Oolite. Principal genera : Cardinia, Anthracosia, 



CavTjonicoIa, A nirplophora. 



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 (Second- 

 ary strata), Anisocardia (Jm-assic), Isocardia, 

 Lihitina, Cored liojihaya ; Basterotia (Eocene), 

 The families Pachydomidae (Palaeozoic) and 

 Megfdodontidae (Palaeozoic — Secondary) are 

 probably related to the Cyprinidae. 



Fam. G. Aetheriidae. — Anal orifice complete, foot absent, la])ial 



Fig. 305. — Isocardia vul- 

 garis Reeve, China. 



