CLASS I 



PELECYPODA 



443 



Area Lain, (type A. noae Linn.). Shell trapezoid, equivalve, with a wide amphi- 

 detic area, distant conspicuous beaks, and radial sculptiu'e ; a wide byssal gape ; a 

 long, straight, transversely dentate hinge line, with many small similar teeth. 

 Tertiary and Recent. Used in the wider sense to include all the groups of Arcidae, 

 there are some 200 living and 300 to 400 fossil species. 



Subgenera : Barbatia Gray (Fig. 662) ; Scapharca, Noetia, Anadara (Fig. 663) and 

 Argina Gray ; Scaphula Benson (fresh-water), etc. 



Isoarca Mlinst. (Fig. 664). Shell smooth, inflated ; beaks full, incurved ; hinge 

 line with rather amorphous dentition. Upper Jura and Lower Cretaceous. 



Fig. 662. 



Area {Larhatia) harbata Linn. Miocene ; 

 Gruiid, near Vienna, i/i- 



Fifi. 603. 



Area (Anadara) diluvii Lain. 

 Pliocene ; Siena. 



Fig. 664. 



Area (Isoarca) cordi- 

 fonnis Ziet. Upper Jura ; 

 Nattheim, WUrtemberg. 



Glycimeris Da Costa (Pectunculus Lam. ; Axinea Poli) (Fig. 665). Rounded and 

 almost symmetrical. Basal margin dentate ; area as in Area, liut shorter ; ligament 



Fio. 665. 

 Glycimeris dbovatus (Lam.). Oligocene ; Weinheim, near Alzey, Hesse, i/i. 



multivincular ; teeth ol)lique, in an arched series, interrupted during growth by the 

 subsidence of the areal margin. Cretaceous to Recent ; maximum in Miocene. 



Section C. Schizodonta Steinmann (emend.). 



Superfamily 3. PTERIACEA DalL 



Shells of varied form, frequently alate, with a nacreous or sub-nacreous inner and 

 prismatic on.ter layer ; the epidermis seldom conspicuous ; area amphidetic ; ligament 

 variable, usually not parivincular ; gills filibranchiate or reticulate, usually reflected; 

 mantle lobes free, without siphons ; pallial line simple ; the anterior addtictor smaller. 



