164 MISSISSIPPIAN BRACHIOPODA 



slightly flattened but not differentiated from the general curvature of 

 the surface; beak smaller than that of the opposite valve and a little 

 more incurved, projecting posteriorly beyond the cardinal line nearly as 

 far as that of the pedicle valve ; cardinal area much smaller than that of 

 the opposite valve, lying in nearly the plane of the valve. Internal 

 characters not observed. 



Surface of both valves marked by fine, rounded, radiating costse of 

 nearly uniform size, which increase by bifurcation and intercalation, from 

 three to four of which occupy the space of one millimeter at the front of 

 a specimen about 20 mm. in length; crossing the radiating costa) there 

 are regular concentric lines of growth which commonly become stronger 

 and more crowded towards the front. The shell substance is pierced by 

 radiating canals or tubules which follow the direction of the costae, along 

 the top of which they open at intervals. 



Remarks. This species resembles S. subelliptica but, besides being 

 larger, it lacks the distinct mesial flattening of the pedicle valve and the 

 slight depression near the front margin. On comparing examples of 

 this species which correspond in size with mature specimens of S. 

 subelliptica, the costee are considerably finer, there being as many as five 

 in the space of one millimeter in an example 12 mm. in length at its 

 front margin. The species differs from S. swallovi in its much smaller 

 size, in the absence of the distinct flattening of the pedicle valve and in 

 the more nearly equal convexity of the two valves. 



Horizon. Chouteau limestone of the Kinderhook. 



SCHIZOPHORIA SEDALIENSIS 11. Sp. 



Plate XXI, Figs. 28-32 



Description. Shell above medium) size, broader than long, subelliptical 

 in outline, the greatest width near the mid-length, hinge-line shorter than 

 the greatest width, cardinal extremities rounded. The dimensions of a 

 nearly complete individual are : length of pedicle valve 30.5 mm., length 

 of brachial valve 30 mm., greatest width 36 mm., length of hinge-line 22 

 mm., thickness 17.8 mm. 



Pedicle valve most convex posterior to the middle, the umbo a little 

 depressed, the surface curving abruptly to the cardinal margin and gently 

 to the lateral and anterior margins, somewhat compressed towards the 

 cardinal extremities; mesial portion of the valve broadly flattened 

 towards the anterior margin; beak small, a little incurved; cardinal area 

 small, sharply defined along its lateral margins, concave, with the curva- 

 ture increasing towards the beak; the delthyrium broadly triangular. 

 Internally the cardinal teeth are supported by short dental plates which 

 are continued as low, angular ridges along the lateral margins of the 

 muscular scars ; muscular scars subovate in outline, less than one-half the 



