868 Report oF THE State GEOLOGIST. 
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 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 
Fic. 509. Stringocephalus Burtini, Defrance. 
Dorsal views of two individuals; showing the differences assumed in growth by the umbo of 
the pedicle-valve. (QUENSTEDT.) 
posteriorly, narrow and sharp on its anterior surface, and pro- 
duced upward and backward into the cavity of the opposite 
valve. At the edge of the median septum of that valve it bifur- 
cates, sending out a short clavate apophysis on either side of it. 
The lateral portions of the hinge-plate begin at the socket-walls 
which are high and narrow, extend downward, inward and for- 
ward 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 brachidium arise at a sharp angle. The latter curve 
backward and outward, and skirt the inner margins of the valves 
120 
