MOLLUSCOIDEA BRACHIOPODA 



SUB-KINGDOM V 



Oehlertella, Hall and Clarke (Lingulodiscina, Whitfield). Much like Schizo- 

 crania, but the ventral valve has concentric growth lines, and no radiating 

 striae. Ventral pedicle area greatly elevated and transected by a narrow 

 open fissure. Devonian to Lower Carboniferous ; North America. 



Schizobolus, Ulrich. Devonian ; North America. (?) Monobolina, Salter. 



Family 2. Discinidae. Gray. 



Derived Discinacea with an open pedicle notch, in early life, in the posterior 

 margin of the ventral valve, which is closed posteriorly during neanic growth, leaving 

 a more or less long, narrow slit, partially closed by the listrium. Ordovician to 

 Recent. 



Orbiculoidea, d'Orbigny (Fig. 512). Shells inequivalved, sub-circular, or sub- 

 elliptical in outline. Apices eccentric. Ventral valve depressed, convex, or" 

 R flattened. Dorsal valve larger, usually de- 



pressed, conical. Pedicle furrow originat- 

 ing behind the apex, extending over a 

 greater or lesser portion of the radius of 

 the valve, and produced at the distal end 

 into a short tubular sipho, emerging on the 

 interior surface near the posterior margin. 

 Surface with fine, crowded or distant, 

 rarely lamellose, concentric lines occasion- 

 ally crossed by radiating lines. Ordovician 

 to Cretaceous ; North and South America, 

 Sub-Carbonifer- Europe, and probably elsewhere. 



A- T TT i TI 



Discina, Lamarck. Very much like 

 Orbiculoidea, but the pedicle emerges through the ventral shell antero- 

 posteriorly,' immediately beneath the beak, instead of through a sipho postero- 

 anteriorly as in that genus. Recent. 



Until recently, Discina embraced all fossil Discinoid shells, but at present 

 this genus seems to be restricted to a single species, 

 D. striata, living off Cape Palmas, West Africa. 



Discinisca, Dall (Fig. 513). Like Orbiculoidea, 

 but with a small septum, as in Discina, behind 

 which is an impressed area, externally concave and 

 internally elevated. This is perforated by a longi- 

 tudinal fissure, extending from a short distance 

 behind the septum nearly to the posterior margin. Peru - , A > Side ^ ie J: v; , ?> ^terior of 



^ ,. ^: wi-.Vi. -, -^ ventral valve. C, Exterior of same. 



FIG. 512. 



Billings). B, 0. nitida, Phill. 



ous ; Missouri, x, Dorsal ; y, Ventral valve, Vi- 



FIG. 513. 

 Discinisca lamellosa, Brod. Recent ; 



Russia and North 



Tertiary to Recent ; North America and Europe. 



Schizotreta, Kutorga. Ordovician and Silurian; 

 America. 



Lindstroemella and Roemerella, Hall and Clarke, are genera related to Orbi- 

 culoidea. Devonian ; North America. 



Superfamily 3. CRANIACEA. Waagen. 



Cemented calcareous Neotremaia without pedicle or anal openings at maturity. 

 Ordovician to Recent. 



