174 



MISSISSIPPIAN BRACHIOPODA 



average size is probably a little less than that of the type specimen whose 

 dimensions have been given. 



Pedicle valve strongly convex, the greatest convexity nearest the mid- 

 dle, the surface strongly arched from beak to front and also transversely, 

 the slope from the umbonal region most abrupt towards the cardinal mar- 

 gin, more gentle to the lateral margins; mesial sinus obsolete in the 

 posterior half of the valve, developed as a broad, shallow depression 

 anteriorly and somewhat produced in front in a lingual extension whose 

 surface is nearly at right angles to the plane of the valve ; beak small-, 

 pointed, incurved; plications obsolete posteriorly, in the anterior half 

 of the shell they are broad and rounded, a single strong one, the strongest 

 one on the valve occupies the median portion of the sinus, and upon each 

 lateral slope of the valve there are two or three weaker ones. Internally 

 a strong median septum is developed, supporting a spondylium, which ex- 

 tends anteriorly from the beak for one-third or one-half the length of 

 the valve. 



FIG. 4. A series of eleven cross-sections of the rostral portion of the shell of 

 Camarophoria explanata (X 2%), showing the spondylium and the manner of 

 development of the cruralium and its relation to the hinge-plate. 



Brachial valve gibbous, more strongly convex than the pedicle, the 

 greatest convexity near the middle, the surface curving steeply from the 

 middle point to the posterior, lateral and antero-lateral margins and more 

 gently to the anterior margin ; mesial fold obsolete in the posterior half 

 of the valve and only moderately elevated in front, it is divided into two 

 rounded folds by a median rounded furrow which originates near the 

 middle of the valve to correspond with the median plication of the sinus 

 of the opposite valve ; the beak is strongly incurved beneath that of the 

 opposite valve ; the plications are similar to those of the opposite valve ; 

 besides the two plications of the fold, already mentioned, there are two 

 or three upon each lateral slope, none of which originate posterior to the 

 middle of the valve and the smaller ones even nearer to the margin. In- 

 ternally this valve has a median septum extending forward from the beak, 

 but it is thinner and more feebly developed than that of the pedicle valve ; 

 it supports the cruralium and the hinge-plate. 



