. 
382 MOLLUSCA SUB-KINGDOM VI 
becoming obsolete in the adult and replaced by the typically Isodont development of the 
crura ; otherwise asin 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- 

Fic. 667. 
Plicatula ectinoides, Lam. Middle 
Lias; Nancy, France. 


Fic. 668. Fic. 669. 
Spondylus spinosus, Sow. sp. Pliiner- Spondylus tenwispina, Sandb. Oligocene; Waldbéckelheim, near 
kalk; Strehlen, near Dresden. 2/s. Kreuznach, Prussia. 1/}. 
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, irreqular, closed, auricles not differentiated, Ostreiform, dimyarian, 
sessile; shell substance sub-nacreous and 
Jibrous ; area amphidetic, obscure ; liga- 
ment obsolete, resiliwm 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 Fic. 670. 
distinct, small ; posterior duplex, larger. Dimya Deshayesiana, Rouault. Eocene; Pyrenees. 
ae ; 2 Inner and outer views of right valve, 3/. (after Rouault). 
Trias to Recent. 







ial 
AN 


i] 


AN) 

2 
Dimya, Rouault (Dimyodon, Mun. Chaln.), (Fig. 670). The recent form inhabits 
deep water. 
Family 36. Limidae. d’Orbigny. 
Shell equivalve, auriculate, gaping, Pectiniform, monomyarian ; shell substance 
Jibrous, 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 filibranchiate, with direct and reflected limbs; foot small 
