' MEDINA SANDSTONE. 5 



382. 1. ARTHROPHYCUS HARLANI. 



Plate I. Fig. 1 Pl. II. Figs. 1 a, 1 b, 1 c. 



Fucoides alleghaniensis & brongniartii. Harlan, Med. and Phys. Researches, p. 393 & 398. 

 J<*. harlani. Conrad, Annual Report on Palaeontology, 1838, p. 113. 



Plant composed of strong rounded and articulated stems, which divide near the base into 

 numerous elongated branches ; branches simple, flexible, articulated and diminishing very 

 gradually, usually appearing of the same dimensions throughout, and more or less curved ; 

 diameter of the branches \ - ^ inch. 



The specimens of this plant, always in fragments, often cover large surfaces of the thin slabs 

 of the Medina sandstone. The more common diameter of the branches is from one-fourth to 

 half an inch, but some of the larger stems often reach an inch in diameter. Fragments are 

 frequently seen of one to two feet in length, and broken at either extremity. Fragments are 

 sometimes found where a strong stem, apparently near the root, divides into several branches 

 near the same point, but these branches are not again found to subdivide. From the condition 

 of the rock, and the few specimens which have been found showing this character, its mode of 

 growth cannot be clearly determined. It must have been exceedingly prolific, since great sur- 

 faces are crowded with its fragments ; and these layers are covered only by a deposition of a 

 few inches, when another growth equally abundant is found upon the succeeding layer. This 

 succession of deposits has gone on through a thickness of many feet ; the surface of each suc- 

 cessive layer, at intervals of a few inches, being covered in a similar manner. In many situations 

 the transverse ridges or articulations are mostly or entirely removed, leaving the surface nearly 

 smooth. The branches are often compressed, and present a longitudinal furrow, which, however, 

 is only accidental. 



Plate I. 

 Fig. 1 . This specimen is a portion of a slab covered with fragments of the branches of this species. 

 Some of them are worn nearly smooth, and others have a longitudinal depressed line. 



Plate II, 

 Fig. 1 a. A fragment, showing the base of a large stem which diverges into numerous branches. 

 Fig. \ b. A. similar fragment, showing a second bifurcation above the first. 



Specimens like the above are of rare occurrence. 

 Fig. 1 c. A fragment of a branch somewhat spirally twisted and flattened. This specimen gives 



evidence that the plant grew in an erect or suberect position, and that the pressure 



from above caused it to assume its present form. The fragment shows also two broken 



stems with bifurcating branches. 



Position and locality. This species occurs abundantly at the falls on the Oswego river, 

 somewhat rarely and imperfectly at Rochester and Brockport, and very abundantly and in fine 

 condition at Medina in Orleans county. It is likewise found at Lockport, and in an imperfect 

 condition near Lewiston. Fine specimens have been obtained along the Welland Canal ( in 

 Canada West), where it cuts through the Medina sandstone. Fine specimens are likewise 

 obtained near Lewistown, Mifflin county, Va. (State Collection.) 



See note at the end of the volume. 



