162 MISSISSIPPIAN BRACHIOPODA 



valve and bordered by elevated margins, divided longitudinally by an 

 elevated ridge upon which are situated the adductor scars. In the brachial 

 valve the socket plates are erect and divergent ; the cardinal process is 

 similar to that of Rhipid.omella but becomes resorbed and narrowed with 

 age ; the muscular scars are quadripartite and much less distinctly denned 

 than those of the pedicle valve. Surface of both valves marked by fine, 

 hollow, tubulose costa?, which are produced into short spines as in 

 Rhipidomella. 



SCHIZOPHORIA SUBELLIPTICA (White and Whitfield) 

 Plate XXIII, Figs. 1-5 



1862. Ortkis subelliptica, White and W T hitfield, Proc. Bost. Soc. Nat. Hist., 



vol. 8, p. 292. 



1870. Orthis subelliptica? Winchell, Proc. Am. Phil. Soc., vol. 11, p. 251. 

 1901. Schizophorm subelliptica Weller, Trans. St. Louis Acad. Sci., vol. 



11, p. 182, pi. 16, figs. 4-5 ; p. 196, pi. 19, figs. 6-7. 



Description. Shell small, broader than long, transversely subelliptical 

 in outline, the greatest width near the mid-length of the shell, the hinge- 

 line about two-thirds the greatest width of the shell, the cardinal ex- 

 tremities rounded. The dimensions of two pedicle valves are : length 

 10.8 mm. and 11 mm., width 13.5 mm and 13.8 mm., length of hinge-line 

 9 mm. and 9 mm., convexity 3.9 mm and 3.9 mm. 



Pedicle valve most prominent on the umbo, curving abruptly to the 

 cardinal margin and gently to the anterior and antero-lateral margins, 

 compressed towards the cardinal extremities; the mesial portion of the 

 valve distinctly flattened anteriorly and usually depressed in an ex- 

 ceedingly shallow, rather broad and ill-defined sinus; the beak pointed, 

 rather prominent, a little incurved; cardinal area of moderate size, con- 

 cave, the curvature increasing towards the beak, the lower, flatter portion 

 lying at nearly a right angle to the plane of the valve, its lateral margins 

 sharply defined. Internal characters not observed. 



Brachial valve not observed. 



Surface marked by fine, rounded, radiating costas, increasing by bifur- 

 cation and intercalation, every second or third one of which is slightly 

 larger, about four or five occupying the space of one millimeter at the 

 front of a mature shell 11 mm. in length. The shell substance pierced by 

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

 the summits of the larger of which, the canals open at irregular intervals. 

 Crossing the radiating costas are regular, concentric lines of growth, 

 usually obscure or obsolete except near the margin where several are 

 crowded together. 



Remarks. In its typical expression this species has been recognized 

 only in the fauna of the Kinderhook oolite bed at Burlington, Iowa, 



