172 MISSISSIPPIAN BRACHIOPODA 



Among the numerous examples of the species which have been exam- 

 ined, a considerable amount of variation is exhibited in the proportional 

 length and breadth of the shells and in the strength of the plications. An 

 occasional example is found upon which the plications are essentially 

 obsolete, and others occur on which they are obsolete towards the beak, 

 but in all other respects, both external and internal, so far as they can be 

 examined, they are identical with the plicated examples, and all are be- 

 lieved to belong to a single species. 



CAMABOPHORIA BISINUATA (Rowley) 

 Plate XXIII, Figs. 20-45 



1900. Seminula bisimiata Rowley, Am. Geol., vol. 25, p. 263, pi. 5, figs. 



21-24. 

 1909. Camarophoria bisinuataf Weller, Bull. Geol. Soc. Am., vol. 20, 



p. 301. 



Description. Shell small, subovate to subpentagonal in outline, more 

 or less subglobular in form, the length greater or a little less than the 

 width, the greatest width near or in front of the middle of the shell. The 

 dimensions of two examples, metatypes, are : length of pedicle valve 9.2 

 mm. and 9 mm., length of brachial valve 8.4 mm. and 8 mm., greatest 

 width 9.8 mm. and 8.3 mm., thickness 6.1 mm. and 6.3 mm. 



Pedicle valve arched from beak to front, moderately convex in the 

 umbonal region, the curvature of the surface is abrupt and somewhat 

 inflected from the umbonal region to the cardinal margin, and more 

 gentle to the antero-lateral margins ; mesial sinus obsolete in the posterior 

 half of the valve, rather broad and shallow anteriorly, deepest towards 

 its lateral margins with a low, broad, rounded fold in the middle, pro- 

 duced anteriorly in a lingual extension whose surface lies at nearly a right 

 angle to the plane of the valve ; beak small, pointed and moderately in- 

 curved; plications wanting except the broad, low, median fold which is 

 usually present in the sinus. Internally, a strong median septum about 

 one-third the length of the valve extends anteriorly from the beak, and 

 supported by this septum is a distinct spondylium. 



Brachial valve more strongly convex than the pedicle, becoming gib- 

 bous in the more globular examples, the greatest depth anterior to the 

 middle and sometimes close to the anterior margin, the surface curving 

 abruptly from the middle to the posterior, lateral and antero-lateral 

 margins ; the median portion of the anterior half of the valve is elevated 

 in a mesial fold which sometimes gives to the anterior portion of the 

 valve a trilobed appearance, along its median line the fold is marked by 

 a furrow which is commonly narrower than the median plication of the 

 opposite valve; the beak is pointed and incurved beneath that of the 

 opposite valve ; plications absent from the lateral slopes as in the pedicle 



