ORDER III PROTREMATA Suey 
Chonostrophia, Hall and Clarke. Like Chonetes, but with the shell reversed 
or concayo-convex. Lower and Middle Devonian ; North and South America. 
Chonetella, Waagen. Upper 
Carboniferous; India. Chonetina, 
Krotow. Permian; Russia. 
Chonopectus, 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 (Orthothriz, ae 
Geinitz ; Leptaenalosia, King), (Fig. A, Chonetes striatella, Dalm.sp. Silurian; Gottland. 1/;. 
530). Shell Productoid in general B, Pisses of dorsal valve of Chonetes (after Davidson). 
- , C. sarcinulata, de Kon, Devonian; Coblenz. 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 


Bet (0; 

A BY . Sea 
Fic. 530, Fic. 531, 
Strophalosia Goldfussi, Miinst. sp. Permian; Gera, Reuss. Productus horridus, Sow. 
A, Dorsalaspect. B, Profile. C, Cast of dorsal valve with brachial Permian; Gera, Reuss. 1/4. 
impressions. Natural size. 
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 ; Arbusculites, 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 
