388 MOLLUSCA SUB-KINGDOM VI 
Ceromya, Ag. (Fig. 689). Cordate, inflated, with rather anterior, prosogyrous 
beaks; hinge margin of the right valve 
superior, edentulous, but with a blunt 

Fia. 687. Fic. 688. 
aor 2 : ; “1G. 689. 
Plewromya tenwistriata, Gresslya_ latirostris, ee 
Ag. Middle Jura, Za- Ag. Lower Oolite; Ceromya, ef. Aalensis, Quenst. Middle Jura; Kneut- 
jaezki, Poland. 1/;. Tannie, Sarthe. 1/;. tingen, Lorraine. Hinge, 1/9. 
elongated process in front of an internal callosity. Chiefly occurring as casts. Jura. 
Family 2. Pholadellidae. Miller (emend.) 
Shells obovate, usually attenuated behind and slightly gaping, hinge margin thin, 
edentulous, ligament parivincular, external ; posterior adductor scar large. Palaeozoic. 
Allorisma, King. Elongate, arcuate, the pallial line sinuated, anterior side 
shorter, sometimes with a lunule; sculpture strongest mesially. Carboniferous and 
Permian. 
Rhytimya, Ulrich. Elongate, sub-quadrate, concentrically waved, the waves 
stronger anteriorly ; sculptured on the posterior half with 
radiating series of granules; lunule very narrow. Silurian. 
Pholadella, Hall; Cimitaria, Hall. Devonian. 
Family 3. Pholadomyacidae. Gray. 
Shell substance nacreous and cellulo-crystalline ; gills com- 
pletely united behind, forming a septum below the anal 

Fic. 690. 
eer ‘1G. 691. IG. 695 
Pholadomya  Murchisoni, Bia, 691 Fia. 692. 
Sow. Middle Jura; Piez- Pholadomya deltoidea, Ag. Pholadomya Puschi, Goldf. Oligocene ; 
chnow, Poland. 1/). Middle Jura; England. 1/5, Tolz, Bavaria, 2/3. 
chamber ; foot small, with an opisthopodium ; siphons long, wnited to their tips, not 
wholly retractile, naked ; ventral commissure of the mantle with a pedal and an opistho- 
