XVI EULAMELLIBRANCHIATA — TELLINACEA 453 



branchial orifice on the ])uccal margin, foot long, broadened, 



with a bj^ssus, animal usually viviparous. Tertiary . 



Genera : Erycina^ KelUa^ Pytliina^ Lasaect., Lepton. 



Fam. 15. G-aleommidae. — Mantle edges more or less re- 

 flected over the shell, apertures and foot as in Erycinidae ; shell 



thin, equilateral, hinge with few teeth or none. Tertiary . 



Genera: G-aleomma., Scintilla^ Sportella^ Cldamydoconclia., Hlnds- 

 iella., Epliippodonta (Fig. 32, p. 81). 



Fam. 16. Cyrenidae. — Siphons short, foot large, no bys- 

 sus ; shell equivalve, subtriangular, with periostracum, hinge 

 with two or three cardinals, laterals present ; animal hermaphro- 

 dite, viviparous. Fresh or brackish water. Jurassic . Gen- 

 era: Cyrena^ Corhicula (subg. Batissa^ Veloynta)^ Sphaerium 

 (= Cyclas)^ Pisidliim^ Galatea^ Flscheria. 



The families Cyrenellidae (single genus, Cyrenellci) and 

 Raiigiidae (single genus, Rangia) are probably to be placed here. 



Sub-order II. Tellinacea. — Siphons long, separate, foot and 

 labial palps ver}" large, pallial sinus deep, two adductor muscles. 



Fam. 1. Tellinidae. — External branchial fold directed 

 dorsally, foot with byssogenous slit, but no byssus, branchiae 

 small ; shell compressed, equivalve, ligament external, at least 



two cardinals in each valve, laterals variable. Cretaceous . 



Principal genera: Tellina (with many sections), G-astrana. 



Fa^ni. 2. Scrohiculariidae. — Animal as in Tellina; shell orbic- 

 ulate or long oval, equi- 

 valve, hinge-teeth weak, 

 ligament in an internal 



cavity. Tertiary . 



Principal genera : Scrohi- 

 cularia., Syndosmya^ The- 

 ora^ Ciimingia^ Semele. 



Fam. 3. Donacidae. — 

 External branchial fold „ „^„ ^ „. , ,, i, , ,:> .t ^• 



Fig. 306. — Tellina rastelluni iianl., East Indies. 



directed ventrally ; shell 



equivalve, subtriangular, solid, smooth, two or three cardinals 



in each valve, laterals variable, ligament external. Jurassic 



^ Genera: Donax, Ipliigenia^ Isodonta. 



Fam. 4. TancredUdae. — Shell donaciform, ligament external, 

 cardinals usually two in each valve, posterior laterals strong. 

 Trias . Genera: Tancredia (Secondary strata), -Sewic?6>naa;. 



