OllDElt III 



PROTHEMATA 



317 



( '/tonostrophia, Hall and Clarke. Like Chonetes, but with the shell reversed 

 or concavo-convex. Lower and Middle Devonian ; North and South America. 



Chonetelltt, \Vaagi-n. Upper 

 Carboniferous ; India. Chonetina, 

 Krotow. Permian ; Russia. 



Chonopectnx, Hall and Clarke. 

 Chonetes-like shells, but cemented 

 ventrally to extraneous objects. 

 External surface reticulated by a 

 double, oblique series of concentric 

 lines and fine radiating striae. 

 Lower Carboniferous ; North 

 America. 



Strophalosia, King (Orthothrix, 



Geillitz; Leptaewlosia, King), (Fig. A.ChrnietesgMotella.D&lm.ap. Silurian ; Gottlaud. J/,. 



530). Shell Productoid in general , {"tenor of dorsal valve of OumetoMtiu Davidson). 



' C, C. sa.rci tnilata, de Kon. Devonian ; Coblenz. 1/1- 



form, cemented by the ventral 



umbo. Both valves with well-defined area and deltidium. Ventral valve 

 with two prominent teeth unsupported by lamellae. Muscular impressions 

 small ; brachial ridges distinct. Surface of ventral valve covered with spines ; 

 that of the dorsal valve either spinous, lamellose, or smooth. Middle 

 Devonian to Permian ; Europe, India, North and South America. 



Aulosteges, Helmersen. Much like Strophalosia, but not cemented by the 



FIG. 529. 

 A, Chonetes striatella, Dalin. sp. Silurian ; Gottlaud. 1/1- 



FIG. 530. 



Strophalosia Goldfussi, Miinst. sp. Permian ; Gera, Reuss. 

 A, Dorsal aspect. B, Profile. C, Cast of dorsal valve with brachial 

 impressions. Natural size. 



FIG. 531. 



Produclus horridus, Sow. 

 Permian ; Gera, Reuss. 1/4- 



ventral umbo ; deltidium covered with small spinules and the surface of both 

 valves thickly set with spines. Permian ; Russia and India. 



Productella, Hall. Shells small, Productoid, with narrow cardinal areas in 

 both valves. Ventral valve with small teeth ; dorsal valve with sockets and 

 crural plates. Brachial impressions distinct. Devonian. 



Productus, Sowerby (Pyxis, Chemnitz ; Arlusculites, Murray; Protonia, Linck ; 

 Marginifera, Waagen), (Figs. 531, 532). Shell without functional pedicle, 

 probably anchored by the ventral spines ; concavo-convex, valves usually 

 produced anteriorly ; outlines semi-circular, sometimes transversely elongate. 

 External surface usually with more or less prominent radiating ribs, which 

 are crossed by concentric lines or wrinkles ; rarely smooth or finely striated. 

 Cardinal areas, teeth, sockets, and crural plates absent or rudimentary. Ventral 

 valve convex, sometimes geniculated ; occasionally with median sinus. Muscular 

 impressions consisting of two dendritic adductors and a pair of broadly flabel- 

 late, striate diductors ; traces of spiral or brachial cavities occasionally 



