346 GEOLOGY OF THE BLACK HILLS. 



BRACHIOPODA. 



LINGULIDJL 



Genus LINGULA Brag. 

 LINGULA BREVIBOSTRIS. 



Plate 3, figs. 4, 5. 



Lingula brevirostris M. & H, Proc. Acad. Nat. Sci. Phil. 1858, p. 50. 



Ibid., Oct, I860, p. 419. 

 Lingula brevirostris M. & H., Pal. Up. Missouri, p. 69, PL 3, fig. 3. 



"Shell subovate, varying to spatulate-ovate, very thin; lateral margins 

 nearly straight or somewhat convex, generally converging a little towards 

 the beaks; front snbtruncate or abruptly rounded; cardinal extremity nar- 

 rowly rounded. Beaks obtuse and apparently not extending beyond the 

 cardinal margin." 



The above is the author's description of the species as given in the 

 Paleontology of the Upper Missouri, so far as it relates to the general form 

 of the shell. The specimens which we have examined correspond very 

 closely with their figures above cited, except that they are not usually as 

 broad, proportionally, as their Fig. 3, but with Fig. 3 a they agree. The 

 sides of the shells are slightly converging above the lower third of the 

 length to the commencement of the cardinal slopes; the beak is obtusely 

 pointed and short; the base rather sharply rounded than otherwise — that 

 is, the curve is not that of a true circle, but rather paraboloid ; but we 

 have seen none of them which might be called subtruncate. The surface 

 of our shells are not polished, being somewhat decomposed or exfoliated 

 by the separation of the rather soft sandstone in which they are embedded. 

 The shells are rather highly convex and somewhat inclined to angularity 

 from the beak to near the middle of the length, below which they become 

 slightly flattened on the central portion, though not enough to modify the 

 form of the front outline. Fine concentric lines mark the surfaces on al) 

 the specimens. 



