498 



MOLLUSCA 



PHYLUM VI 



Subgenera : Hemimaetra Swains. ; Leptospisula Dall ; Cymbophora Gabb ; ScJdzodcsma Gray. 

 Mulinia Gray. Ligament and resilium immer8ecl in the same socket. Miocene 

 and Recent. 



•Rangia Desm. (Gnathodon Gray, non Goldfuss). Like Mulinia, Init witli 

 elongated laterals, and the anterior lateral hooked at the umbonal end. Estuarine. 

 Pteropsis Conrad. Eocene. Lahiosa (Schmidt) Moller. Miocene and Recent. 

 Ltotraria Lam. (Fig. 825). Soleniform, hinge Mactroid. Tertiary and Recent. 

 Schizothacrus Conr. {Tresus Gray) ; Eastonia Gray ; Heferocardia Desh. Tertiary 

 and Recent. Zenatia Gray ; Anatinella Sow. Recent. 



Family 39. Cardiliidae Dall. 



Shell cordiform, with prominent prosogyrous heahs, small, thin, radially sculptured ; 

 posterior adductor scar impressed upon a radial myoplioric lamina, the anterior scar 

 elongated, pallial line not sinuated ; ligament external, seated on nymphs ; resilium 

 internal connecting projecting chondrophores ; hinge without laterals, hut the cardinal 

 teeth as in Mactra. Tertiary to Recent. 



Cardilia Deshayes. Eocene and Recent. 



Family 40. Mesodesmatidae Deshayes. 



Shell solid and heavy, usually Donaciform, with 

 erect or opisthogyrate beaks, otherwise as in the Mactridae; 

 siphons naked, not united. Tertiary to Recent. 



Mesodesma Desh. Tertiary and Recent. Mac- 

 tropsis Conr. Eocene. Atactodea Dall {Paphia 

 Lam. ; Eryx Swains.) ; Davila Gray ; Anapella Dall. 

 Recent. Ervilia Tnrton (Fig. 826). Tertiary and 

 Recent. Gaecella Gray. Recent, fluviatile. 



Pig. 820. 



Ervilia podolica Eicli w. Miocene (Sar- 

 matian Stage) ; Wicseii, near Vienna. Vl- 



E. ASTHENODONTA. 



Hinge often essentially Mactroid, hut usually degenerate or obsolete, owing to modi- 

 fications induced by the burrowing habit. 



Superfamily 16. MYACEA Menke (emend.). 



Burrotving, long siphoned, frequently inequivalve Pelccijpods, visually with the mantle 

 lobes largely united below, more or less united siphons, and degenerate hinge apparatus. 



Family 41. Myacidae Woodward. 



Shell substance cellulo-crystalline, earthy, with a conspicuous epidermis ; valves un- 

 equal, more or less elongate, rounded in front 

 and gaping behind ; adductor scars suh- 

 equal ; pallial line sinuated ; shell margins 

 plain ; area obsolete or none ; ligament and 

 resilium internal, opisthodetic, attached in 

 the left valve to a projecting chondrophore 

 merging with the dorsal margin behind, and 

 in the right valve to an inconspicuous, 

 usually sub-umboncd chondrophore; hinge 

 edentulous ; siphons united, with a horny 

 tunic, not wJluIIu retractile. Tertiary and ,_ ... „, ., /r^i • i r, ■. % 



' -^ - Mya arcnaria Linn. Pleistocene (Glacial Deposits) 



Recent. Bohuslim, Sweden. 



