ORDER TV 



TELOTREMATA 



33!) 



Sub- equally biconvex shells with concentric growth lines extended into 

 lamellae. Ventral urnbo not prominent, incurved, usually concealing the 



FIG. 581. 



)tna tumida, Dalm. sp. Silurian ; Gottland. --1, Shell of the natural size. B, Interior of ventral valve- 

 C, Hinge-line and median septum of dorsal valve. 



pedicle opening and deltidial plates. Teeth supported by dental lamellae. 

 Hinge-plate of the dorsal valve perforated by a "visceral foramen." The 



Fio. 582. 



ntrica, von Buch sp. A, Shell with dorsal valve partly removed. B, Interior of dorsal valve, 

 1/1. C, D, Frontal and lateral aspect of spiralia (after Davidson). 



Devonian and 



con- 



peculiar jugum of this genus is illustrated in Fig. 582, 6', D. 

 Carboniferous. Distribution general. 



Actinoconchus, M'Coy. Athyroids with very wide radially striate 

 centric lamellae. Carboniferous ; Europe. 



Cleiothyris, King. Athyroids with concentric rows of flat spinules. Car- 

 boniferous and Permian. Distribution general. 



Seminula, M'Coy. Smooth-shelled Athy- 

 roids. Dorsal hinge-plate very prominent. 

 Carboniferous. Distribution general. 



SpirigereUa,W8AgeiL Carboniferous ; South 

 America and India. 



Amphitomella, Bittner. Smooth - shelled 

 Athyroids with a double cardinal process and 

 median septa in each valve. Alpine Trias. 



Tetradinella, Bittner (Plicigera, Bittner), (Fig. 583). Athyroids with 

 four corresponding ribs on each valve. Alpine Trias. 



Pentadinella, Bittner. Athyroids with five corresponding ribs on each 

 valve. Alpine Trias. 



Anomadinella, Bittner. Athyroids with a number of angular alternating 

 ribs towards the anterior margins. Alpine Trias. 



FIG. 583. 



Ti'tr<'i-t;,i<U" triiinni'llo, Schlotll. 



Muschelkalk ; Recoaro, Italy, i/l- 



