BRACHIOPODA. 
125 
of the deltidial plate is a narrow and rather abrupt flattening of the shell, 
suggestive of a cardinal area. The umbonal cavity is short and usually 
much contracted, leaving only a simple passage for the pedicle. The 
teeth are approximate and prominent, arising from the bottom of the 
valve, and above the hinge-line curved backward and toward each other, 
making a very close and firm articulation with the other valve. The 
dental lamellae are not continued along the interior of the valve. The 
muscular area is well defined and consists of a deep posterior area, in front 
of which lies a flabelliform scar, extending for fully one-half the length of the 
shell. 
In the brachial valve the beak is not prominent and the false area is 
absent. A small chilidium is present and lies against the vertical pos¬ 
terior wall of the hinge-plate. The hinge-plate is greatly elevated, rest¬ 
ing upon two stout supports which are placed very closely together, 
leaving no opening between them at the bottom of the valve. The 
upper face of the plate is quadrate, but very deeply divided by a median longi¬ 
tudinal groove, and less conspicuously, by a transverse groove; the surface is 
thus divided into four parts, two posterior portions which extend backward into 
the umbonal cavity of the opposite valve, as short, stout horns, and two ante¬ 
rior processes which are broader but equally elevated, the crura arising from 
the ante-lateral margins of the latter. In the deep longitudinal cleft or groove 
of the plate is a short, convex lobe, terminating posteriorly in a simple or 
double extremity; sometimes this part is absent. The whole process is ren¬ 
dered more prominent by being slightly constricted about its base. It is sup¬ 
ported interiorly by a short median septum, which is frequently obsolete. The 
dental sockets are small and deep. The crura are broad, thin and compara¬ 
tively short, uniting with the primary lamellae in a sharp lateral curve 
without diminution or increase in size. The umbonal blades are not greatly 
incurved and are quite as narrow as any portion of the primary ribbon. The 
loop takes its origin well forward near the middle of the spiral cones; the lat¬ 
eral branches are somewhat broadened at their origin, but become slightly 
constricted and twisted just above their bases, and then widen again, attaining 
