382 



MOLLUSCA 



SUB-KINGDOM VI 



becoming obsolete in the adult and replaced by the typically Isodont development of the 



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



Plicatula, Lam. (Harpax, Park), (Fig. 667). 

 Shell compressed, with coarse radial, often divari- 

 cate ribbing, a small area, and long shallow crenulate 

 crural teeth, diverging at a sharp angle. Trias to 

 Recent ; maximum in Jura and Cretaceous. 



Spondylus, Linn. (Figs. 668, 669). Shell in- 

 flated, with radial, often spiny or foliaceous sculp- 



Plicatnla pectinoides, Lam. 

 Lias ; Nancy, France. 



Sj)ondylus tenuispina, Sandb. 

 Kreuznach, Prussia. 



Oligocene ; Waldbockelheim, near 



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

 Jura to Recent ; maximum from the Tertiary onward. 



? Pachypteria, de Kon. Carboniferous. P. nobilissima, de Kon. 



Family 35. Dimyidae. Dall. 



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

 sessile ; shell substance sub-nacreous and 

 fibrous ; area amphidetic, obscure ; liga- 

 ment obsolete, resilium alivincular, in- 

 ternal; hinge armature Taxodont, obsolete; 

 crural development feeble; gills fili- 

 branchiate, the inner direct filaments 

 wanting, the outer not reflected; foot 

 and byssus absent ; anterior adductor FIG- 670. 



distinct, small; posterior duplex, larger. _ Dimya Deshuyesiana, Rouault. Eocene; Pyrenees. 



Trias to Recent. 





, . 



Inner a'nd outer views of right valve, 3/ 2 (after Rouault). 



Dimya, Rouault (Dimyodon, Mun. Chalm.), (Fig. 670). The recent form inhabits 

 deep water. 



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, equal in both valves; ligament alivincular, 

 resilium sub-internal; gills Jilibranchiate, with direct and reflected limbs; foot small 



