CLASS I PELECYPODA 499 



Mya Liiiii. (Fig. 827). Smooth externally. Tertiary and Recent. 



Siibgenera : Platyodon Conrad. Surface dccussated, siphou with horny appendages. 

 Cryptomya Conrad. Small, the pallial line discrepant in the two valves. Sphenia Turton. 

 Minute, byssiferous, nestling. Tugonia Gray. Tertiary and Recent. 



Family 42. Oorbulidae Fleming. 



Shell small, much as in Mya, hut the pallial line feeble or obsolete, the ligament 

 usually suh-external, separated from the resilium, which is internal, alivincular and 

 amphidetic ; the chondrophore 

 is received into a socket of the 

 opposite valve, not merged with 

 the valve margin ; hinge lüith 

 one or two sub-umhonal pro- 

 jecting teeth, and rarely ohscure 

 traces of laterals ; the posterior 

 gape inconspicuous ; siphons 

 short, united, naked, wholly 

 retractile. Trias to Recent. 



Fio. 828. 



Corbukt (Bicorbula) gallica La in. 

 Calcaire Giossier; Damery, near 

 Epernay, France. Hinge, i/i. 



Fio. 829. 



A, Corbula carinata Duj. 

 Miocene; Pötzleinsdorf, oear 

 Vienna. B, C. angjisUUa Sow. 

 Upper Cretaceous ; Gosau. 



Corbula Lam. (Figs. 828, 

 829). Small, ovate, rostrate, very inequivalve, the riglit valve convex, larger, with a 

 prominent tooth in front of the pit for the resilium, left valve with a flattened 

 chondrophore, and usually a posterior tooth. Trias to Recent. 



Subgenera : Erodona Daudin {Azara d'Orb. ; Potamomya Sow. ). Pallial sinus obsolete, 

 fluviatile. Pleistocene and Recent. Bothrocorbula Gabb. With a lunule deeply indented 

 into tlie cavity of the valves. Tertiary and Recent. Corhulamella Meek. With an anterior 



myophore. Cretaceous. Aniso- 

 Ä thyris Conr. (Pachydon Gabb). 



Pliocene. Paramya Conr. ; Cor- 

 hulomya Nyst. Tertiary and 

 Recent. 



Family 43. Saxicavidae 



Gray. 



Shell substance as in Mya ; 

 epidermis conspicuous ; valves 

 equal, free, rüde and often 

 irregulär, more or less elon- 

 gated and gaping, not fully 

 covering the animal ; adductor 

 scars often irregulär, the pallial 

 line discontinuous or irregulär, 

 the sinus distinct ; shell mar- 

 gins smooth; area obsolete; 

 ligament and resilium external, 

 parivincular, seated on strong 

 nymphs, sometimes widely ex- 

 tended ; hinge without laterals^ 

 with few feeble or obsolete sub- 

 umbonal cardinals. Creta- 

 ceous to Recent. 



Saxicava Fleuriau (Glycimeris Schum. ; Hiatella Daudin ; Byssomya Cuvier ; 

 Agina Turton). Hinge edentulous in the adult, with one or two caitlinals in the 



Panope msnardi Desh 

 of valves. B, Internal mould 



Miocene; Vienna Basin. A, Dorsal view 

 C, Hinge-plate seen from above, V2' 



