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 



Pleuromya tenuistriata, 

 Ag. Middle Jura, Za- 

 jaczki, Poland, ifr. 



Fio. CSS. 



Gresslya latirostris, 

 Ag. Lower Oolite ; 

 Tannie, Sarthe. 1/1- 



Ceromya, cf. Aalensis, Quenst. Middle Jura ; Kneut- 

 tingen, Lorraine. Hinge, 1/3. 



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 cellule-crystalline; gills com- 

 pletely united behind, forming a septum below the anal 



FIG. (590. 

 Pholadomya Murchisoni, 



Sow. Middle Jura: 

 chnow, Poland, l/i- 



Piez- 



Fio. 691. 



Pholadomya deltoidea, Ag. 

 Middle Jura ; England. 1/2- 



FIG. 602. 



Pholadomya Puschi, Goldf. Oligocene ; 

 Tb'lz, Bavaria. . 



chamber; foot small, with an opisthopodium ; siphons long, united to their tips, not 

 ivholly retractile, naked ; ventral commissure of the mantle with a pedal and an opistho- 



