498 



MOLLUSCA 



PHYLUM VI 



Subgenera : Hemimactra Swains. ; Leptospisula Dali ; Cymbophora Gabb ; Schizodesma Gray. 



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

 and Recent. 



Rangia Desni. (Gnathodon Gray, non Goldfuss). Like Mulinia, but with 

 elongated laterals, and the anterior lateral liooked at the umbonal end. Estnarine. 



Pteropsis Conrad. Eocene. Xak'om (Schmidt) Möller. Miocene and Recent. 



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



Schizothaerus Conr. {Tresus Gray) ; Eastonia Gray ; Heterocardia Desli. Tertiary 

 and Recent. Zenatia Gray ; Änatinella Sow. Recent. 



Family 39. Oardiliidae Dali. 



Shell cordiform, with prominent prosogyrous heahs, small, thin, radially scu^Jtured ; 



^rior adductor scar impressed upon a radial myophoric lamina, the anterior scar 

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

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

 teeth as in Mactra. Tertiary to Recent. 



Gardilia Deshayes. Eocene and Recent. 



Family 40. 



Fig. 826. 



Ervilia podolica Eichw. Miocene (Sar- 



matian Stage) ; Wiesen, near Vienna. Vi- 



Mesodesmatidae Deshayes. 



Shell solid and heavy, usually Donaciform, with 

 erect or opisthogyrate heahs, otherwise as in the Mactridae; 

 Siphons naked, not united. Tertiary to Recent. 



Mesodesma Desh. Tertiary and Recent. Mac- 

 tropsis Conr. Eocene. Ätactodea Dali (Paphia 

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

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

 Recent. Gaecella Gray. Recent, fluviatile. 



E. ASTHENODONTA. 



often essehtially Mactroid, hut usually degenerate or ohsolete, owing to modi- 

 fications induced hy the hurroiving hahit. 



Superfamily 16. MYACEA Menke (emend.). 



Burrowing, long siphoned, frequently inequivalve Pelecypods, usually with the mantle 

 lohes largely united helow, more or less united siphons, and degenerate hinge apparatus. 



Family 41. Myacidae Wood ward. 



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

 equal, more or less elongate, rounded in front 

 and gaping hehind ; adductor scars suh- 

 equal ; pallial line sinuated; shell margins 

 piain ; area ohsolete or none ; ligament and 

 resilium internal, opisthodetic, attached in 

 the left valve to a projeding chondrophore 

 merging with the dorsal margin hehind, and 

 in the right valve to an inconspicuous, 

 usually suh-umhonal chondrophore; hinge 

 edentulous ; siphons united, with a horny 

 tunic, not wholly retradile. Tertiary and 

 Recent. 



Fig. 827. 



Mya arenaria Linn. Pleistocene (Glacial Deposits) 

 Bohuslän, Sweden. 



