BRAcHIOPODA. 867 
(?) Cryptacanthia, White and St. John. 1867. 
~Shells small’ plano-convex or naviculoid. Loop long and 
recurved ; jugal processes united above. (?) Outer margins of the 
brachidium covered with spines. 
Fic. 508, 
Cryptacanthia compacta, White and St. John. 
A copy of the original figure. 
(Ware and St. Jon.) 
Type, Cryptacanthia compacta, White and St. John. 
Distribution. Carboniferous. 
Stringocephalus, Defrance. 1827. 
(emend. Sandberger. 1842.) 
Shells varying in outline from transverse to elongate-oval ; 
biconvex, the brachial valve being somewhat the deeper; the 
greater convexity is in the umbonal region, giving to the brachial 
valve a high-shouldered appearance. 
On the pedicle-valve the beak is somewhat narrow, its apex 
being abruptly attenuate, acute and often greatly incurved. From 
beneath the beak diverge two sharp ridges extending to the 
extremities of the hinge, and delimiting the broad cardinal exca- 
vations which seem to constitute a true cardinal area. The del- 
thyrium is broad and triangular ; in young shells it may be wholly 
open or incompletely closed by the imperfectly developed deltidial 
plates, while at maturity it is closed, with the exception of a cir- 
cular foramen, and in old shells the deltidial plates are anchylosed, 
forming ajsingle plate which becomes incurved, and the foraminal 
passage is thus obscured, and may take the form of a tube or 
sheath prolonged into the umbonal cavity. 
On the interior the teeth are short, free and curved upward at 
their extremities. In the middle of the valve is a vertical longi- 
tudinal septum, which extends from the beak to near the anterior 
margin. This septum is short and thick posteriorly, but becomes 
119 
