BRACHIOPODA. 799 
and rather abrupt flattening of the shell, suggestive of a cardinal 
area. The umbonal cavity is short and usually much thickened, 
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 lamellz are not continued over the interior 
of the valve. The muscular area is well defined and con- 
sists 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 posterior wall of the hinge-plate. The hinge-plate is 
greatly elevated; it rests 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 quad- 
rate, but very deeply divided by a median longitudinal groove, 
and less conspicuously by a transverse groove; the surface isthus 
divided into four parts, two posterior portions which extend 
backward into the umbonal cavity of the opposite valve, as 
short, stout horns, and two anterior processes which are 
broader but equally elevated; from the ante-lateral margins 
of the latter arise the crura. In the deep, longitudinal 
cleft or groove of the plate is a short, convex lobe, termi- 
nating posteriorly in a simple or double extremity; some- 
times this part is absent. The whole process is rendered 
more prominent by being slightly constricted about its base. It is 
supported interiorly by ashort median septum, which is frequently 
obsolete. The dental sockets are small and deep. The crura are 
broad, thin and comparatively short, and unite with the primary 
lamellze 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 jugum 
takes its origin well forward near the middle of the spiral cones; 
the lateral branches are somewhat broadened at their origin, but 
become slightly constricted and twisted just above their bases, 
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