386 



MOLLUSCOIDEA 



PHYLUM V 



Strophomena Blainville. Shells like Bafinesquina, but with the relative con- 

 vexity of valves reversed, and the ventral muscular area sharply limited by 



an elevated margin. Ordovician ; America 

 and Europe. 



Schuchertella Girty (Fig. 570). Much like 

 Strophomena. Shell piano -convex, concavo- 

 convex or biconvex. Surface covered with 

 radiating Striae, which are convoluted by 

 sharp concentric lines. Cardinal area of 

 ventral valve prominently developed and not 

 attached by cementation ; dorsal area narrow. 

 Dental plates rudimentary. Cardinal process 

 united to crural plates, the whole forming 

 a vertical subcrescentic process. Muscular 

 impressions flabelliform. Silurian to Upper 

 Carboniferous ; North and South America, 

 Europe and India. 

 Like Schuchertella, but with the muscular areas 

 Lower Devonian ; North America. 



Fig. 570. 



Schuchertella umhraculum (Schloth.). 

 Devonian ; Gerolstein, Eifel. Natural size. 



Hipparionyx Vanuxem. 

 much larger and no dorsal cardinal area. 



Schellwienella Thomas (Orthothetes Waagen, non Orthotetes Fischer) (Fig. 571). 



Fig. 571. 



Schellwienella crenistria (Phill.). Lower Carboniferous; Wexford. A, Muscular portion of vential valve. 

 B, Interior of dorsal valve. A, A', Adductors ; R, Diductors ; j, Cardinal process; d, Uental sockets (after 

 Davidson). 



Near Schuchertella, but with short diverging dental plates and the cardinal area 

 either rudimentary or absent, Lower Carboniferous ; Europe. 



Kayserella Hall and Clarke. Small Schuchertella-like shells, with a very 

 high dorsal median septum. Devonian ; Germany. 



Orthotetes Fischer. Like Schuchertella, but in the ventral valve there is a 

 small triangulär umbonal Chamber formed by the uniting of the dental plates, 

 in front of which is a well-developed median septum. Ventral cardinal area 

 usually attached by cementation. Upper Carboniferous and Permian ; North 

 and South America, Europe, India and Russia. 



Derlya Waagen. Like Orthotetes, but without the umbonal Chamber. 

 Lower and Upper Carboniferous; North and South America, Europe and 

 India, 



Omionia Caneva. Related to Orthotetes as Geyerella is to Meekella. Permian ; 

 Italy. 



