54 MISSISSIPPIAN BRACHIOPODA 



g-eneric name Schellivienella. The most essential characters of Schuchert- 

 dla are the biconvex shell and the undeveloped dental plates. The last 

 of these characters cannot always be detected in the specimens studied, 

 but so far as has been observed these two characters are always asso- 

 ciated. 



SCHUCHERTELLA PERNGLENENSIS n. Sp. 



Plate III, Figs. 12-13 



1909. Orthothetes rubra Weller, Bull. Geol. Soc. Am., vol. 20, pi. 12, 

 fig. 4 (not fig. 5). 



Description. Shell above medium size, biconvex, broader than long, 

 the hinge-line a little less than the greatest width of the shell, in mature 

 examples the cardinal extremities obtusely angular. The dimensions of 

 the holotype are : length 35.5 mm., greatest width 52 mm., length of hinge- 

 line about 42 mm., height of cardinal area 6 mm. 



Pedicle valve very gently convex, most prominent in the umbonal 

 region, sloping with a very gentle curvature to the anterior and lateral 

 margins, very slightly or not at all flattened towards the cardinal ex- 

 tremities; mesial sinus absent; beak blunt, not incurved, cardinal area 

 flat, with sharply defined lateral margins, sloping posteriorly from the 

 hinge-line; delthyrium broadly triangular, broader than high, closed by 

 a convex deltidium with a sinuate cardinal margin. 



Brachial valve aparently somewhat less convex than the pedicle, with 

 the surface flattened towards the cardinal margin. 



Surface of both valves marked by narrow, subangular costae, which 

 increase by implantation, the intercostal spaces being wider than the costae 

 themselves, one or two costa3 occupying the space of one millimeter. The 

 costae are crossed by rather strong, irregularly developed, concentric lines 

 of growth. Very fine concentric markings are faintly indicated on some 

 portions of the shell and probably covered both valves when in a perfect 

 condition. 



Remarks. The holotype of this species is a specimen preserving both 

 valves which have been somewhat crushed longitudinally. It was at 

 first thought to be an example of 8. rubra, and was originally illustrated 

 as such, but the difference in the character of the radiating costae is so 

 marked that it is now described as the type of a distinct species. Besides 

 the difference in the radiating costae, the specimen is considerably larger 

 than any example of 8. rubra which has been studied. The internal 

 characters of neither valve have been observed, and the cardinal margin 

 of the brachial valve has been pushed in behind the cardinal area of the 

 pedicle valve in such a manner as to hide the characters of that portion 

 of that valve. It is believed that the- most important distinguishing 

 character of the species, by means of which it may be separated from 



