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 j^rominent, 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 lamellce 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 



