CLASS I 



PELECYPODA 



441 



Leda Sclium. (Figs. 655, 656). Shell rostrate, elongate, often keeled, concentri- 

 cally striate ; hinge as in Nucula ; pallial sinus small. Silurian to Recent. 



o 



.Fin. (555. 



Lrda rostral a 

 (Lam.). MiiWle Jura; 

 Milhaud, Aveyron. 



Vi- 



Fig. fibii. 



Leda deshayesiana Ducli. 

 Oligocene ; Rupelmonde, 

 Belgium. '^|■^. 



Fig. 657. 



Yoldia arctica Gray. 

 Pleistocene ; Bohus- 

 lan, Sweden. Vi- 



Fl(i. 6.58. 



Nucnllna oinlis 

 (Wood). Miocene; 

 Forchtenau, near 

 Vienna. 



Yoldia Moller (Fig. 657). Shell thin, wide, and more or less gaping behind, 

 hinge as in Nucula. Cretaceous to Recent. 



Nuculina d'Orl). (Fig. 658). Nuculiform, hinge teeth few and discrepant; with 

 large lateral tooth and external ligament. Tertiary and Recent. 



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

 without internal chondrophore. Tertiary and Recent. 



Superfamily 2. ARC ACE A Deshayes. 



Shell of varied fornij usually 'with a pilose epidermis, porccllanous, with tubuliferous 

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

 multivincular ; gills filihranchiate, with the filaments ustially reflected ; mantle lobes 

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

 marine or fluviatile. 



Family 11. Parallelodontidae DalL 



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

 hinge mtirgin ; ligament m,ultivincular. Carboniferous to Recent. 



The ancient forms of this group appear to connect 

 with tlie Pteriacea through Ptcrinea, and with Area 

 through CucuUaea. The Recent forms, which from 

 their shell characters have been referred to Macrodon, 

 are all small and probably .sliould be referred to the 

 Arcidae. The relationship of this family to the 

 Arcidae is very intimate but not exclusive. 



Parallelodon Meek (Macrodon Lycett) (Fig. 

 659). Shell elongate, sul)- quadrate, with am- 

 phidetic area, and 

 j)rominent, rather 

 anterior beaks. 

 Anterior teeth 

 transverse or flex- 

 uous, posterior long 

 and parallel to the 

 hinge line. Devon- 

 ian to Tertiary ; 

 maximum in Coal Fig. 659. 



Measures. Parallelodon hirsonensis Morri.s and ■^'"' ^^^' 



n^rint^r^^ntr^^^,,-, ^^^^ C^reat Oolite ; Minclilnlianipton, CmulUuaTierMlia iVOrh. Oxfonlian ; Vieil 

 IrrammatOdon England. Vi- St. Remy, Ardennes. Vi- 



