214 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



and parallel to one a nother ; woody axis of the larger branches and stems 

 comparatively small, in the ultimate smaller branches apparently wanting, 

 these being composed seemingly of a succulent material, which was cov- 

 ered by a dense, durable epidermis ; fruit not seen. 



The stems and branches of this plant, originally cylindrical, are now 

 from pressure always found flat. The stems and larger branches are gen- 

 erally found decorticated or deprived of their epidermis. The removal of 

 the epidermis carries away the scale-like leaves, and on the smallest ulti- 

 mate twigs they in such cases leave no scars But when the stems and 

 largest branches are deprived of their epideraiis and not decorticated, 

 rhombic or triangular scars mark the place of the leaves on the joints. 

 The larger twigs quite often are arranged on the main stems in an umbel- 

 late manner. In other cases the branches are arranged in the same plane 

 and go off alternately 



The genus Frenelopsis, as hitherto known, is composed of only two 

 species, viz, F. Eoheneggeri Schenk, and F. occidentalis Heer. The former 

 is, according to Schenk, the most abundant plant in those beds in which it 

 occurs. He gives in Die Foss. Pflanzen dei' Wernsdorf Schichten, the most 

 complete description and delineation of this species known. We may then, 

 in our comparative study of this Potomac species, confine ourselves to 

 Schenk's figures and description. Schenk, in his description of the leaves, 

 says (page 13) that they occur in pairs opposite to each other, the succeed- 

 ing pairs being decussate. The leaves of one of the Potomac species cer- 

 tainly occur in whorls of three, and, judging from the figures given by 

 Schenk, I am inclined to think that the leaves on F. Hoheneggeri occur also in 

 threes on the joints. In PI. VI, Fig. 6, in Scheldt's work, the pair of leaves in 

 the middle of the stem seem to present on the front aspect of the twig the 

 greater portion of their width, and by their position strongly suggest that 

 they are opposed behind by a single leaf, which belongs to the same whorl. 

 The lower leaf on this twig, by its eccentric position, indicates that it is 

 opposed behind by two leaves. The position of the pair above mentioned 

 is quite similar to that seen in some specimens of the Potomac plant F. 

 ramosissima, where the pair is opposed by a single leaf. If this be the 

 true character of the arrangement of the leaves, then Schenk's opinion, ex- 



