CLASS I 



PELECYPODA 



459 



hecoming obsolete in the adiUt and re-placed hy the tyjncally isodont develo^ment of the 



crura ; otherivise as in the Pectinidae. Trias to Recent. 



Plicatula Lam. {Harpax Park.) (Fig. 716). Shell 

 conipressed, with coarse radial, often divaricate 

 ribbiiig, a small area, and long shallow crenulate 

 crural teeth, diverging at a sharp angle. Trias to 

 Recent ; inaximum in Jura and Cretaceous. 



Spondijlus Linn. (Figs. 717, 718). Sliell inflated, 

 with radial, often spiny or foliaceous sculpture ; 



Fio, 716. 



Plicatula 2)ectinoides Lara. Middle Lias ; 

 Nancy, France. 



Fio. 717. 



Spondylus spinosus (Sow.). Plänerkalk ; 

 Strehlen, near Dresden. 2/3. 



Fio. 718. 



Sptondylus tenuisplna Sandb. Oligocene ; Waldböckelheim, near 

 Kreuznach, Prussia. 1/1. 



Jura 



attached valve with a conspicuous area ; crural teeth heavy, short, smooth. 

 to Recent ; maximuin from the Tertiary onward. 



(?) Pachijpteria de Koninck. Carboniferous. P. nobilissima (de Koninck). Pro- 

 spondylus Zinimerin. Pennian and Trias. Philippiella Waagen. Alpine Trias. 



Family 35. Dimyidae Dali. 



Shell inequivalve, irregulär, closed, auricles not differentiated, Ostreiform, dimyarian, 

 shell suhstance suh-nacreous and 



fihrous ; area amphidetic, ohscure ; liga- 

 ment obsolete, resilium alivincular, in- 

 ternal; hinge armature taxodont, obsolete; 

 crural development feeble; gills fili- 

 branchiate, the direct filaments not 

 reflected; foot and byssus absent ; an- 

 terior adductor distinct, small ; posterior 

 duplex, larger. Trias to Recent. 



Dimya Rouault {Dimyodon Mun.- 

 Chalni.) (Fig. 719). The Recent forms inhabit deep water. 



Fio. 719, 



Dimya deshayesiana Rouanlt. Eocene ; Pyrenees. Inner 

 and outer views of right valve, 3/2 (alter Rouault). 



Family 36. Limidae d'Orbigny. 



Shell equivalve, auriculate, gaping, Pectiniform, monomyarian ; shell substance 

 fibrous, with minute tubules, not nacreous or prismatic ; hinge edentulous, or with traces 

 of taxodont armature; area amphidetic, eqiial in both valves ; ligament alivincular, 



