332 GEOLOGY OF THE BLACK HILLS. 



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

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

 Black Hills. 



Genus PAL^OPHYCUS Hall. 



PAL^OPHYCUS OCOIDENTALIS. 



Plate 1, fig. 3. 



Palceophycus occidentalis Whitf., Prelim. Eept. Pal. Black Hills, 1877, p. 7. 



Remains consisting of strong, subcylindrical, flexuous stems or roots, 

 covering the surface of the sandstone. The stems are more or less rounded, 

 although frequently quite flattened, and varying in diameter from one-fourth 

 of an inch to one inch, frequently bifurcating and sometimes dividing into 

 threes. They are commonly interlaced with each other, but do not appear 

 to coalesce, but are simply overlapped; the surfaces, although sometimes 

 quite smooth, are generally marked by indistinct, longitudinal pits and 

 ridges of greater or less extent, frequently occurring of an inch in length, 

 while many are merely short, roughened depressions, which give a corru- 

 gated surface to the stems. 



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 occasionally 

 one will be found to terminate in an obtuse point. 



This species bears some resemblance to Fucoides duplex Hall (Foster and 

 Whitney Lake Superior, p. 226, Plate A 23, Fig. 1), but does not present the 

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

 cation. It is very similar to P. tubularis Hall, from the Calciferous sand- 

 stone of New York ; but is less ridged, and has a somewhat different 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 examined, how- 

 ever, 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 Eedwater Valley, 

 Black Hills. 



