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. 
TV. Isoponra. Fischer. 
Superfamily 7. PECTINACEA. Reeve. 
Shell usually inequivalve, flabelliform, more or less auriculate, and monomyarian ; 
shell structure sub-nacreous, corrugated, and rarely prismatic, 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 tnner 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- 
ectous ; 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 im 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, Frech (Lyrio- 
Fic. 659. pecten, Hall). Devonian. 
Aviculopecten papyraceus, Sow. ; : . : 
Coal Measures ; Werden, West- Crenipecten, Hall (Pernopecten, Winch.) Like Aviculo- 
yhalia. ‘ : . ; 
: pecten, but with a Taxodont hinge. Carboniferous. 
The preceding genera lead up to the prototypes of Pteriidae as a radical for the present 
family. 
Pecten, Miiller (Vola, Mérch ; Janira, Schum. ; Neithea, Droult), (Fig. 660). Shell 
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. 

The above diagnosis is of the Fic. 660. Fic. 661. 
sub-genus Pecten s. s. In a wide Pecten quinquecostata, Sow. Pecten (Chlamys) subtextorius, 
sense all the species of Pecten are Cenomanian; Rouen. 1/}. Goldf. Coral-Rag; Nattheiimn. 
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, and 

Ae 
