ORDER III 



TELEODESMACEA 



401 



Family 11. Monopleuridae. Fischer. 



Shell substance without canals ; shell sessile, closed, very inequivalve ; free valve with 

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

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

 detic. Cretaceous. 



Monopleura, Math. (?Dipilidia, Math.), (Figs. 720, 721). Very iiii-ijuivalvi-, .-month 

 or ribbed ; dentition always inverse ; attached by tin- right valve, which may be either 



FIG. 720. 



Monopleura trilolita, d'Orb. Neocomian (Sclirattenkalk) ; Orgon, 

 Vaucluse. 1/1- A, , Anterior and posterior views. C, Interior of 

 attached valve. 



Monopleura varians, Math. Ur- 

 gonian ; Orgon, Vaucluse. Interior 

 of both valves. Vi- 



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

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



Valletia, Mun. - Chalin. Neocomian. Gyropleura, Douville. Cenomanian to 

 Senonian. Bayleia, Mun. -C halm. Turonian. B. Pouechi, Mun.-Chalm. 



Family 12. Caprinidae. D'Orbigny. 



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

 prismatic; valves heavy, irregular, unequal, closed; free valve spiral, cardinal for/mil" 



FIG. 7-22. 



Longitudinal section of 

 the, fixed valve of Caprina 

 <"/' rxii, showing cavities in 

 the inner shell layer. 1 



FIG. i 



Cross -section 

 of the free valve 

 of Caprina com- 

 ni. n ni.", .showing 

 parallel canals 

 in the middle 

 layer. 



FIG. 



Plagioptychus Aguilloni, d'Orb. Upper Cretace- 

 ous ; Gosau, Austria. 2/ 3 . 



101, with a posterior myophoric crest for the adductor ; fixed valve conical or spiral, 

 cardinal formula 010 ; ligament in a deep groove, almost internal, parivincular, opistho- 

 detic. Cretaceous. 



Caprina, d'Orb. (Gemmellaria, Mun.-Chalm.; Cornucaprina, Futt), (Figs. 722, 723). 

 VOL. I 2 D 



