ORDER I PRIONODESMACEA. 381 
cannot properly be regarded as of generic value. The most familiar of the groups thus 
named are as follows :— 
Chlamys, Bolten (Palliwm, Schum. ; Decadopecten, Riipp.), (Figs. 661, 662). Shell 

Fic. 664. 
Frc. 662 SPE pee P. (Entoliwn) 
Nie Pecten (Camptonectes) lens, cornutus, Quenst. 
Pecten (Chlamys) varius, Linn. Sow. Middle Jura; Balin, Upper Jura; Ho- 
Pliocene ; Rhodes. : near Cracow. 1/}. henzollern. 1/;. 
radially sculptured, nearly equivalve, with small, unequal ears, and deep byssal notch with 
well-developed ctenolium. Trias to Recent. 
Camptonectes, Ag. (Fig. 663). Shell small, thin, nearly smooth, with fine divergent 
striation radiating from a median line. Jura to Recent. 
Entoliwm, Meek (Fig. 664). Smooth, thin, with sub-equal ears diverging at a sharp angle 
above the beaks ; byssal notch obsolete. Carboniferous to Cretaceous. 
Pseudamusium, Adams. Shell small, thin, glassy ; the posterior ear obsolete, byssal notch 
distinct. Cretaceous to Recent. Syneyclonema, Meek is scarcely different. 


Fic. 666, 
Bs Hinnites abjectus, Phill. sp. 
Fic. 665. Middle Jura; Balin, near 
Amusium cristatus, Bronn sp. Miocene; Baden, near Vienna, 1/,. Cracow. 1/3. 
Amusium, Schum. (Fig. 665). Shell with raised radial riblets internally; externally 
smooth or delicately sculptured ; valves large, flattish, with sub-equal ears ; byssal notch 
inconspicuous or absent. Lias to Recent. 
Sub-genus : Propeamusium, Greg. Small, thin, abyssal ; often with relatively conspicuous 
sculpture, usually discrepant on the valves. Tertiary and Recent. 
Hinnites, Defr. (Fig. 666). Shell free and Pectiniform when young, later adherent 
to other objects and more or less distorted. Trias to Recent. 
Pedum, Brug. Shell with an alivincular ligament in an open groove and area like 
that of Spondylus in the adult; the young like Chlamys. Recent ; sessile in corals. 
Family 34. Spondylidae. Fleming. 
Shell inequivalve, nearly equilateral, closed, Pectiniform, obscurely wuriculate, mono- 
myarian ; sessile; area wmphidetic, much larger on the attached valve; ligament alivincular, 
resilium more or less submerged ; byssus obsolete; hinge with a Taxodont provinculum, 
