BRACHIOPODA. 
283 
extends from the beak to near the anterior margin. This septum is short and 
thick posteriorly, but becomes thinner and higher towards the front, ending 
abruptly in the pallial region. 
In the brachial valve the umbo is obtuse. The cardinal area is distinctly 
developed and divided by a very broad triangular fissure, the covering of which 
(chilidium) is frequently retained, much modified by the presence of the great 
Fig. 203. Stringocephalus Burtini, Defrance. 
Dorsal views of two individuals; showing the differences assumed in growth by the umbo of the pedicle-valve. 
(Quenstedt.) 
cardinal process. The dental sockets are comparatively shallow. The general 
form of the hinge-plate is triangular, with its apex anterior; its central portion 
is separated from the narrow, blade-shaped lateral divisions and is produced 
into a great cardinal process, rounded posteriorly, narrow and sharp on its 
anterior surface, and produced upward and backward into the cavity of the 
opposite valve. At the edge of the median septum of that valve it bifurcates, 
sending out a short clavate apophysis on either side of it. The lateral por¬ 
tions of the hinge-plate begin at the socket-walls which are high and narrow, 
extend downward, inward and forward to the anterior extremity of the plate, 
whence they curve upward into the crura. The crura are long, broadened and 
curved upward towards their extremities where the primary arms of the bra- 
chidium arise at a sharp angle. The latter curve backward and outward, and 
