ORDER II ANOMALODESMACEA 389 
podial foramen. Shell thin, equivalve, gaping, edentulous, or with an obscure sub- 
umbonal tubercle; ligament, and resilium external, opisthodetic, seated. on nymphae ; 
area obsolete or obscure, not amphidetic; beaks entire; pallial sinus well marked ; 
marine. Trias to Recent. 
Pholadomya, Sow. (Figs. 690-692). Shell thin, sub-ovate, with radial and con- 
centric sculpture, inflated, and with rather prominent beaks; hinge edentulous, or 
with an obscure thickening; scars feeble, pallial sinus moderately deep. In the 
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Fic. 693. 
a aie ees een G. 694. 
Goniomya Duboisi, Ag. Inferior Oolite; Bayeux, Higs6 
Calvados. A, Shell, 1/3. B, Surface showing Homomya (Arcomya) caleeiformis, Ag. Inferior 
punetations, magnified. Oolite ; Les Moutieux, near Bayeux, Calvados. 2/3. 
> Oo > 2 
posterior dorsal region the radial sculpture is usually feeble or absent. Lower Lias to 
Recent ; formerly very abundant, but now represented by but a single species from 
the Antilles. 
Procardia, Meek. Includes those forms with an escutcheon. Jura. 
Goniomya, Ag. (Fig. 693). With V-shaped sculpture. lias to Cretaceous; very 
plentiful in Middle and Upper Jura. 
Homomya, Ag. (Arcomya, Myopsis, Ag. p.p.), (Fig. 694). Distinguished from the 
typical Pholadomyas by its smooth or very finely sculptured shell, without ribs. 
Trias to Cretaceous. 
(?) Machomya, Plectomya, Loriol; Mactromya, Ag. Jura and Cretaceous. 
Family 4. Anatinidae. Dall. 
Soft parts like Pholadomya, the foot small and grooved, ventral foramina small, and 
the siphons with a horny integument, not entirely retractile. Shell sub-equivalve, truncate, 
or gaping behind, edentulous, the resiliwm internal between 
two spoon-like chondrophores vertically directed and often 
supported by buttresses ; ligament obsolete or absent ; area 
obsolete ; beaks transversely fissured ; pallial sinus well 
marked ; monoecious; marine. Jura to Recent. 

Anatina, Lam. (Platymya, Cercomya, Ag.; Plicomya, 
Fic. 695. 
Stol.), (Fig. 695). Shell thin, nearly equivalve, con-  Anatina producta, Zittel. Upper 
centrically but feebly sculptured, posterior side shorter Cretaceous; Gosau Valley, Austria. 
than the anterior. Jura to Recent. 
Periplomya, Anatimya, Conrad ; Rhynchomya, Agassiz. Cretaceous. 
Family 5. Periplomidae. Dall. 
Shell sub-nacreous, conspicuously inequivalve, nearly closed, edentulous ; the resilium 
internal, between two anteriorly or vertically directed chondrophores, often buttressed, the - 
lithodesma rarely wanting; ligament and area absent; beaks fissured ; pallial sinus 
