66 MISSISSIPPIAN BRACHIOPODA 



ized by the form of the brachial valve which has its greatest convexity 

 farther forward than is usual in members of the genus, so that the 

 curvature to the anterior margin is somewhat more abrupt than to the 

 hinge-line. The pedicle valve resembles that of 8. inflatus, but the beak 

 seems to be more depressed, the brachial valves of the two species, how- 

 ever, are very different. The usual absence of concentric growth lines 

 is a noticeable character of the species. The two valves have not been 

 observed in articulation, but both occur in such close association in the 

 limestone as to leave no doubt as to their being parts of the same species. 

 Horizon. Kinderhook. 



SCHELLWIENELLA ALTERNATA n. sp. 



Plate IV, Fig. 6 



Description. Shell rather large, broader than long, the hinge-line a 

 little shorter than the greatest width, the cardinal extremities angular. 

 The dimensions of a nearly complete brachial valve are : length 41.5 mm., 

 width 57 mm., length of hinge-line 51.5 mm., convexity 11.8 mm. 



Pedicle valve not observed. 



Brachial valve convex, the greatest convexity anterior to the middle, 

 the surface curving with a more abrupt slope to the front margin than 

 to the cardinal margin, compressed and subauricular towards the cardinal 

 extremities, the umbonal region depressed convex or nearly flat; the 

 mesial portion of the valve somewhat flattened from the beak to the front 

 margin but not distinctly differentiated from the general curvature of 

 the surface; the beak inconspicuous, not produced beyond the cardinal 

 margin. 



Surface of the shell marked by a series of stronger, rounded, radiating 

 costae, averaging a little less than 1 mm. apart at the shell margin, alter- 

 nating with which there are usually very much finer and more angular 

 costs. The costae are crossed by fine, concentric markings which are 

 stronger in the intercostal furrows, being nearly obsolete on the summits 

 of the costas. A few stronger concentric lines of growth are also present 

 at intervals. 



Remarks. This species is based upon a single, nearly complete brachial 

 valve, no pedicle valve having been found which can be associated with 

 it. This valve somewhat resembles S. planumbona in its distinctly flat- 

 tened umbonal region, but it is proportionally broader, besides having 

 distinctly different surface markings. The distinctly alternating costae 

 with the concentric markings stronger in the intercostal furrows are 

 characters not shared with any other species of the genus here described. 



In the absence of the pedicle valve it is not possible to determine cer- 

 tainly the true generic relations of this species, and it may eventually 

 prove to be a member of the genus Schuchertella. The species has been 



