quently occurring of an inch in length, while many are merely short, 

 roughened depressions, which give a corrugated surface to the sterns. 



Judging from the specimens in the collection, we should suppose they 

 often attain considerable length, as on a specimen measuring nearly ten 

 inches the variation in diameter is scarcely perceptible, but occasion- 

 ally one will be found to terminate in an obtuse point. 



This species bears some resemblance to Fucoides duplex Hall, (Post. & 

 Whit., Lake Sup., p. 226, pi. A., 23, fig. 1,) but does not present the 

 longitudinal depression along the middle as in that one, except near a 

 bifurcation. It is very similar to P. tubularis Hall,. from the Calciferous 

 Sandstone of Ke\y York ; but is less ridged and has a somewhat differ- 

 ent mode of bifurcation from any of the specimens of that species which 

 we have seen. If a larger number of the New York species were ex- 

 amined, however, it is possible that the resemblance might be much 

 greater than at present supposed. 



Formation and locality. In the plant beds of the Potsdam formation 

 (probably Upper Potsdam or Calciferous). Head of Bed Water Valley, 

 Black Hills, Dakota. 



MOLLUSCOIDA. 



BRACHIOPODA. 



LlNGULEPIS CUNEOL.US, n. sp. 

 Plate 2, figs. 5 and 6. 



Shells small, rather below the medium size, triangularly ovate in out" 

 line, or sometimes subcuneate ; ventral valve triangularly ovate, with 

 a sharp somewhat pointed beak, the width and length about as three 

 and four, and the point of greatest length near the lower third of the 

 length of the valve; cardinal slopes abrupt, scarcely convex; basal line 

 rounded at the sides but nearly straight in the middle ; surface of the 

 valve strongly convex, becoming almost subangular in the upper part 

 dorsal valve much shorter, proportionally, than the ventral, the length 

 but little exceeding the width ; sides and base more rounded and the 

 beak truncate ; surface distinctly convex. 



Surface of the shell apparently smooth, but usually exfoliated, in 

 which condition a few fine radiating lines are visible. 



The shell differs from L. pinnaformis Ovven, in size and in the more 

 distinctly cuneate form of the ventral valve. At first sight, it might be 

 taken for the young of that species, but a little critical examination 

 soon reveals marked distinctions in the truncation of the front margin, 

 and especially in the form of the cardinal slopes, which are rounded 

 and never concave, as in almost all ventral valves of that species. In con- 

 sequence of this latter feature, the beak does not appear so attenuated 

 as in that one, although proportionally quite as long. In the general 



