CLASS I 



PELECYPODA 



443 



Area Lani. (type A. noae Liiin.). Shell trapezoid, eqiiivalve, with a wide amphi- 

 detic area, distant conspiciioiis Ijeaks, and radial sciilpture ; a wide l)yssal gape ; a 

 long, straiglit, transversely dentale hinge line, with niany sniall siniilar 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 speeies. 



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

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



Isoarca Münst. (Fig. 664). Shell smooth, inflated ; beaks füll, incurved ; hinge 

 line with rather aniorphous dentition. Upper Jura and Lower Cretaceous. • 



Fig. 662. 



Area (Barhatia) harhata Linn. Miocene ; 

 Grund, iiear Vienna. i/j. 



Fig. 603. 



Area {Anadara) diluvii Lam. 

 Pliocene ; Siena. 



Pio. 664. 



Area (Isoarca) cordi- 

 formis Ziet. Upper Jura ; 

 Nattheim, Würtemberg. 



V,. 



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

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



Fig. 665. 

 Glycimeris dbovatus (Lam.). Oligocene ; Weinheim, near Alzey, Hesse. Vi- 



multivincular ; teeth oblique, 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 Dali. 



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

 prismatic outer layer ; the epidermis seldom conspieuous ; area amphidetic ; ligament 

 variable, usually not parivincular ; gills filihranchiate or reticulate, usually reßected ; 

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



