CLASS I 



PELECYPODA 



441 



Leda Scliuiu. (Figs. 655, 656). Shell rostrate, elongate, often keeled, conceiitri- 

 cally Stria te ; liiiige as in Nucida ; pallial siiius siiiall. Siluriaii to Receiit. 



• Fio. 655. 



Leda rostrata 

 (Lam.). Middle Jura; 

 Milhaud, Aveyron. 



Vi. 



Fio. 650. 



Leda desJiayesiana Duch. 

 Oligocene ; Rupelmonde, 

 Belgium. i/j. 



Yoldia arctica Gray. 

 Pleistocene ; Bohus- 

 län, Sweden. i/i- 



Fig. 658. 



NucuUna ovalis 

 (Wood). Miocene; 

 Forchtciiau, near 

 Vienna. 



Yoldia Moller (Fig. 657). • Sliell tliin, wide, and niore or less gaping beliind, 

 hinge as in Nucula. Cretaceous to Recent. 



Nuc'idina ^^Ov\). (Fig. 658). Nuculiform, hinge teethfew and discrepant ; with 

 large lateral tootli and external ligament. Tertiary and Recent. 



Malletia Desm. and Tindaria Bell. Yoldiform and nnculiforni respectively, but 

 without internal chondrophore. Tertiary and Recent. 



Superfamily 2. ARCACEA Deshayes. 



Shell of varied form, usually with a pilose epidermis, porcellanous, with tiihiiliferous 

 non-prismatic external layer ; area typically amphidetic, ligament external, ali- or 

 multivincular ; gills filibranchiate, with the filaments usually reflected ; mantle lohes 

 free, without siphons, the pallial line simple; foot variable, deeply grooved, hyssogenous ; 

 marine or fluviatile. 



Family 11. Parallelodontidae Dali. 



Shell arciform, with the posterior hinge teeth elongated, tending to he parallel to the 

 hinge margin ; ligament multivincular. Carhoniferous to Recent. 



The ancient forms of this group appear to connect 

 with the Pteriacea through Fterinea, and with Area 

 through Cucullaea. The Recent forms, which froni 

 their shell characters have been referred to Maerodon, 

 are all small and probahly should be referred to the 

 Arcidae. The relationship of this family to the 

 Arcidae is very iutimate but not exclusive. 



Parallelodon Meek {Maerodon Lycett) (Fig. 

 659). Shell elongate, snl)-qnadrate, with ani- 

 phidetic area, and 

 prominent, rather 

 anterior beaks. 

 Anterior teeth 

 transverse or flex- 

 uous, posterior long 

 and parallel to the 

 hinge line. Devon- 

 ian to Tertiary ; 

 maximum in Goal 

 Measures. 



Grammatodon 



Parallelodon hirsonensi.i Morris and 

 Lyc. Great Oolite ; Minchinlianii)ton, 

 England. Vi- 



Fio. 6ö0. 

 CmnUaea hersilüi d'Orb. Oxford ian 

 St. Reniy, Ardennes. Vi- 



Vieil 



