478 



MOLLUSCA 



PHYLUM VI 



attached valve deeper and larger, tlie free valve flatter ; margiiis usually cross-striated, 

 surface lamellar or spinöse ; adductor scars large, not elevated. Cretaceous to Recent; 

 maximum in Eocene. 



Fig. 768. 

 Chama squamosä Lam. Eocene ; Hampshire, i/j. 



Echinochama Fiscli. Nepionic shell elongated, liaving the form, liinge and otlier 

 cliaracters of Gardita ; attaclied when adolescent, free in the yoiing and adult stages. 

 Valves sub-equal and similar; surface vermiculate, spinöse, witli radial ribs. Oligocene 

 and Recent. 



Family II. Monopleuridae Fischer. 



Shell suhstance loiihout canals ; shell sessile, closed, very inequivalve ; free valve ivith 

 the cardinal formula 101, operculiform or slightly spiral ; fixed valve with the formula 

 010, conical, unrolled or spiral; area wanting ; ligament external, parivincular, 

 opisthodetic. Cretaceous. 



Monopleura Math. (? Dipilidia Math.) (Figs, 769, 770). Very inequivalve, smooth 

 or ribbed ; dentition always inverse ; attached by the right valve, v^^hich may be either 



Fig. 769. 



Fig. 770. 



Monopleura trüobita d"Orb. Neocomian (Schrattenkalk); Orgon, Monopleura varians Math. Ur- 



Bouches-du-ßhone. i/i. A, B, Anterior and posterior views. C, Interior gonian ; Orgon, Bouches-du-Rhone. 

 attached valve. Interior of both valves. i/^. 



twisted or coniform ; left valve conical or flat ; ligament as in Chama ; posterior 

 adductor scar buttressed. Lower Cretaceous ; Southern Europe and Texas. 



Valletia Mun.-Chalm. Neocomian. Gyropleura Douville. Cenomanian to 

 Senonian. Bayleia Miin.-Chalm. Turonian. B. pouechi Mun.-Chalm. 



Family 12. Caprinidae d'Orbigny. 



Shell suhstance internally furnished with large parallel canals, the external layer 

 valves heavy, irregulär, unequal, closed ; free valve spiral, cardinal formula 



