ORDER IIl TELEODESMACEA 421 
Family 39. Cardiliidae. Dall. 
Shell cordiform, with prominent prosogyrous beaks, small, thin, radially sculptured ; 
posterior adductor scar impressed upon a radial myophoric lamina, the anterior scar 
elongated, pallial line not sinuated ; ligament external, seated on nymphs ; resiliwm 
internal connecting projecting chondrophores ; hinge without laterals, but 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 opisthoqyrate 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, Turton (Fig. 777). Tertiary and — /rvilia Podolica, Kichw. Miocene (Sar- 
Recent. Caecella, Gray. Recent, fluviatile. quia ae) 3) Weeseny Meat View nat. cd: 

KE. AstTHENODONTA. 
Hinge often essentially Mactroid, but usually degenerate or obsolete, owing to modr- 
fications induced by the burrowing habit. 
Superfamily 16. MYACEA. Menke (emend.) 
Burrowing, long siphoned, frequently inequivalve Pelecypods, usually 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 sub- 
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- 
umbonal chondrophore ; hinge edentulous ; 
siphons united, with a horny tunte, not wholly 
retractile. Tertiary and Recent. 
Mya, Linn. (Fig. 778). Smooth ex- 
ternally. Tertiary and Recent. 

Fic. 778. 
Mya arenaria, Lin. Pleistocene (Glacial Deposits) ; 
Bohuslan, Sweden. Sub- genera: Platyodon, Conr. Surface 
decussated, siphon with horny appendages. 
Cryptomya, Conr. Small, the pallial line discrepant in the two valves. Sphaenca, Turton. 
Minute, byssiferous, nestling. Z'ugonia, Gray. Recent. 
Family 42. Corbulidae. Fleming. 
Shell small, much as in Mya, but the pallial line feeble or obsolete, the ligament 
usually sub-external, separated from the resiliwm, which is internal, alivincular, and 
