BRacHIOPoDA. 827 
in such a manner as to form an elongate cavity, which does not 
extend to the bottom of the valve. Each branch of the septum 
supports one of the lateral divisions of the hinge-plate, to which 
are attached the curved crural processes. In normal conditions 
of development the median interspace of the hinge-plate is not 
closed. The dental sockets bordering the hinge-plate are crenu- 
lated in the typical species. There is no cardinal process. 
In the pedicle-valve slender vertical lamellae support the 
rather small teeth and extend well into the cavity of the valve, 
inclosing a deep and narrow pedicle-scar. 
Type, Camarotechia congregata, Conrad (sp.). 
Distribution. Lower Silurian — Lower Carboniferous. 
Subgenus Plethorhynchus, Hall. 1893. 
(Plate 48, figs. 10-15.) 
Large, ponderous and ventricose shells in which the lateral 
parts of the hinge-plate become united, closing the triangular 
septal cavity but forming no cardinal process. Dental lamelle 
faint, evident only in young shells; teeth large and stout, rest- 
ing on the lateral walls of the valve. 
(Type, Plethorhynchus speciosus, Hall. Oriskany sandstone.) 
Subgenus Liorhynchus, Hall. 1860. 
(Plate 43, figs, 16-24.) ~ 
Shells having the plications on median fold and sinus highly 
developed, but those on the lateral slopes usually faint or 
obsolete. Internal structure as in Camaroraonia ; adductor scars 
on the brachial valve forming a narrow, elongate-oval impression 
divided by the median septum. 
(Type, Liorhynchus quadricostatus, Vanuxem (sp.). Devonian — 
Carboniferous.) 
Wilsonia (Quenstedt), Kayser. 1871. 
(Plate 44, figs. 1-5.) 
Shells with subcuboidal or subpentahedral contour, fold and 
sinus not sharply developed except at the anterior margin, 
abrupt anterior slope, sharply serrated lateral margins of con- 
tact and low surface plications, each of which, on the front of 
both valves, is marked by a fine median line. Dental plates. 
79 
