380 



MOLLUSCA 



SUB-KINGDOM VI 



gyrous, nearly terminal ; teeth striated ; adductor scars strong, with buttressing ridges. 

 Lias to Recent ; abundant in Jura and Cretaceous, very sparse in later .horizons. 



IV. ISODONTA. Fischer. 



Superfamily 7. PECTINACEA. Reeve. 



Shell usually inequivalve, flabelliform, more or less auriculate, and monomyarian ; 

 shell structure sub-nacreous, corrugated, and rarely prismaMc, occasionally tubular ; area, 

 when present, amphidetic ; ligament amphidetic, alivincular ; gills filibranchiate, free, the 

 filaments with or without a reflected limb ; mantle lobes free, without siphons, usually with 

 ocelli, papillae, or other tactile prominences along the margin, and with an inner pro- 

 jecting lamina (curtain] near the margin, at right angles to the plane of the valves ; pallial 

 line simple ; foot small, usually sub-cylindrical, grooved, and byssiferous ; usually mono- 

 ecious ; marine. 



Family 33. Pectinidae. Lamarck. 



Shell inequivalve, inequilateral, auriculate, usually closed, monomyarian, usually 

 free; area amphidetic or obscure; ligament obsolete externally, the immersed portion 

 forming an internal resilium, provinculum Taxodont in the 

 very young, obsolete later, the crural teeth feeble or not developed. 

 Silurian to Recent. 



Aviculopecten, M'Coy (Fig. 659). Shell Pectiniform, 

 radially sculptured. Hinge margin long, feebly auriculate ; 

 ligament in numerous shallow grooves radiating to ' the 

 amphidetic margin of the area. Silurian to Carboniferous. 



Sub-genera : Pterineopecten, Hall ; Orbipecten, Freeh (Lyrio- 

 pecten, Hall). Devonian. 



Crenipecten, Hall (Pernopecten, Winch.) Like Aviculo- 

 pecten, but with a Taxodont hinge. Carboniferous. 



The preceding genera lead up to the prototypes of Pteriidae as a radical for the present 

 family. 



FIG. 659. 



papyraceus, S 



Coal Measures ; Werden, We 

 phalia. 



Pecten, Miiller (Vola, Morch 

 nearly equilateral, very in- 

 equivalve, sub - symmetrical, 

 with well-developed, sub-equal 

 ears; one valve (usually the 

 right) more convex than the 

 other ; interior of the valves 

 not lirate ; hinge with a strong 

 medial internal resilium, on 

 each side of which interlock- 

 ing crural ridges and grooves 

 radiate in the adult ; byssal 

 notch inconspicuous. Cretace- 

 ous to Recent. 



Janira, Schum. ; Neithea, Droult), (Fig. 660). Shell 



FIG. 660. 



Sow. 



Pecten (Clilamys) snlrfextorius, 

 Goldf. Coral-Rag ; Nattheiia. 



The above diagnosis Is of the 



sub-genus Pecten s. s. In a wide p ec ten quinqmcostata, 

 sense all the species of Pecten are Cenomanian ; Rouen. 1/1- 

 free and auriculate, and without 



internal lirae. They have been divided into an excessive number of sections according to 

 the superficial shell characters, but these rarely march with anatomical differences, arid 



