BRACHIOPODA. 



283 



extends from the beak to near the anterior margin. This septum is short and 

 thick f)osteriorly, but becomes thinner and higher towards the front, ending 

 abruptly in the palUal 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, StriiigocephaXus Burtini, Defrance. 

 Dorsal views of two individuals; showing Die diUerences assumed in growtli 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 



