CLASS I 



PELECYPODA 



487 



Sphaera Sow. (Palaeocorhis Conr.). Lower Civl;i(((.us. Sjihaeriola Stol. Trias 



to Cretaceoiis. Fimhriella Stol. Chalk of Britaiii. Gorbicella Mor. and Lyc. Jura. 



M'utiella Stol. (Fig. 796). Anterior cardinal border corriigated, uptiirned ; 



posterior rectilinear, horizontal, witli a feeljlc lalcial tootli. Upper CretrOceous. 



Family 19. Diplodontidae Dali. 



Shell sub-circular in outline, rarely nestling and irregulär ; hinge with the laterals 

 obscure or absent, and the valve margins piain ; the adductor scars continuous peripher- 

 ally with the pallial line ; soft parts like the Lucinidae, but with the external limb of the 

 gills developed, and the anal foramen not tubulär. (?) Jura, Cretaceous to Recent. 



Diplodonta Bronn (Fig. 797). Thin-shelled, orbicular, convex, concentrically 

 striate or pustulose ; cardinals 2 : 2, tlie left anterior and riglit posterior l)iM ; 

 laterals obscure or absent. Tertiary and Recent. 



Ungulina Daudin. Nestling and often ir- 

 regulär. Felania Recluz. Shell conipressed ; 

 feeble laterals present. Axinopsis Sars ; Sphae- 

 rella and Tenea Conrad. Cretaceous to Recent. 



Family 20. Oyrenellidae Fischer. 



Diplodonta dilatata Phill. Plioceiie ; 

 Hhodes. Vi- 



Shell as in Diplodonta, but loith a con- 

 spicuous epidermis ; pallial area smooth ; pallial 

 line not sinuate ; hinge without lateral laminae ; the cardinals like Diplodonta, or 

 with two cardinals in each valve soldered to each other dorsally ; cardinal formula 



RTmmn' ^'^^ anterior left cardinal usually obsolete. Pliocene to Recent, in fresh and 



brackish water. 



Cyrenoida Joannis (Gyrenella Desh.). Pliocene of Florida, Recent in the Antilles 

 and West Africa. 



Joannisiella Dali. Hinge as in Diplodonta, resilium immersed, the larger cardinal 



)ifid, the teeth not soldered above. Cardinal formula 



LlOlO 



Roior 



Recent ; Philippines. 



Family 21. Thyasiridae Dali. 



Shell substance earthy, ivith inconspicuous epidermis and prosocoelous beaks ; valves 

 equal, free, closed, ivith piain margins, smooth, or with feeble 

 concentric Striae, and usually with a radial posterior ßexure ; 

 adductors Lucinoid, pallial area often punctate ; ligament and 

 resilium parivincular, opisthodetic, sub - external, seated in a 

 groove ; area impressed ; hinge feeble without lateral laminae, 

 edentulous, or with an obsolete cardinal tooth in the right valve. 

 Cretaceous to Recent. 



Thyasira Leach (Gryptodon Turton ; Axinus Sow.; Con- 

 chocele Gabb) (Fig. 798). Smooth, thin-shelled, living in 

 deep water. Cretaceous to Recent. 



Philis Fisch, Lunule deeply indented, projecting sj^oon- 

 like into the cavity of the valves. Recent. 



Fio. 79S. 



A, Thyasira sinuosa (Don.). 

 Miocene ; Grund, near Vienna. 

 Vi- B, T. unicarinata Nyst. 

 Oligocene (Septaria - clay) ; 

 Freien wal<le, near Berlin. 



Superfamily 8. LEPTONACEA Dali. 



37te incurrent and excurrent openings between the mantle lohx "/ 

 body, the former anterior. 



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mh nl Ihr 



