a 
364 MOLLUSCA ‘ SUB-KINGDOM VI 
Yoldia, Moller (Fig. 608). Shell thin, wide, and more or less gaping behind, 
hinge as in Nucula. Cretaceous to Recent. 

pes 

Fic. 606. 
Fic. 609. 
Leda rostrata, Lam. Fic. 607. Fic. 608. Nuculina ovalis, 
sp. Middle Jura; Leda Deshayesiana, Duch. Yoldia arctica, Gray. Wood sp. Mio- 
Milhaud, Aveyron. Oligocene ; Rupelmonde, Pleistocene; Bohus- cene; Forchtenau, 
If}. Belgium. 1/;. lan, Sweden. 1/4. near Vienna. 
Nuculina, dOrb. (Fig. 609). Nuculiform, hinge teeth few and discrepant ; 
with large lateral tooth and external ligament. Tertiary and Recent. 
Malletia, Desm., and Tindaria, Bell. Yoldiform and Nuculiform respectively, but 
without internal chondrophore. Tertiary and Recent. 
Superfamily 2. ARCACEA. Deshayes. 
Shell of varied form, usually with a pilose epidermis, porcellanous, with tubuliferous 
non-prismatic external layer ; area typically amphidetic, ligament external, ali- or multi- 
vincular ; gills filibranchiate, with the filaments usually reflected ; mantle lobes free, without 
siphons, the pallial line simple; foot variable, deeply grooved, byssogenous ; marine or 
Auviatile. 
Family 11. Parallelodontidae. Dall. 
Shell Arciform, with the posterior hinge teeth elongated, tending to be parallel to the 
hinge margin ; ligament multivincular. Carboniferous to Recent. 





Fia. 610. 
Parallelodon Hirsonensis, Morris and 
Lye. Great Oolite ; Minchinhampton 
England. 1/. 
+] 
The ancient forms of this group appear to connect 
with the Pteriacea through Pterinea, and with Arca 
through Cucullaca. The recent forms, which from 
their shell characters have been referred to Macrodon, 
are all small and abyssal. The relationship of this 
family to the Arcidae is very intimate but not 
exclusive. 

Parallelodon, Meek (Macrodon, Lycett), (Fig. _ me ae ais 
610). Shell elongate, sub-quadrate, with amphi- Vid te Being Aecektes tie Oxfordige 
detic area, and prominent, rather anterior beaks. 
Anterior teeth transverse or flexuous, posterior long and parallel to the hinge line. 
Devonian to Tertiary; maximum in Coal Measures. 
