no. 1821. REVISION OF POTOMAC PLANTS— BERRY. 297 



ARTHROTAXOPSIS EXPANSA Fontaine. 



Arthrotaxopsis expansa Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 1890, p. 241, 

 pi. 113, figs. 5, 6; pi. 115, fig. 2; pi. 117, fig. 6 (not pi. 135, figs. 15, 18, 22, 

 which are referred to Sphenolepis kurriana (Dunker) Schenk). — Fontaine, in 

 Ward, Monogr. U. S. Geol. Surv., vol. 48, 1906, pp. 504, 520, 546, 571 (not 

 pp. 533, 535, 538, 555, 573, pi. 109, figs. 12, 13, which are referred to Sequoia 

 ambigua Heer, and p. 547, which is referred to Widdringtonites ramosus (Fon- 

 taine) Berry. 



Taxodium (Glyptostrobus) expansum Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 

 1890, p. 252, pi. 123, fig. 1. 



Glyptostrobus expansus Ward, Monogr. U. S. Geol. Surv., vol. 48, 1906, p. 543. 



Sphenolepidium sternbcrgianum densifolium Fontaine, in Ward, Monogr. U. S. 

 Geol. Surv., vol. 48, 1906, p. 524 (part), pi. 112, fig. 11 (not figs. 1, 10). 



Glyptostrobus brookcnsis Fontaine, in Ward, Monogr. U. S. Geol. Surv., vol. 48, 

 1906, pp. 483, 486, 520 (not the other citations). 



Description. — Branches and twigs elongated and extremely slender, 

 widely spreading and sparingly branched, showing a tendency as 

 preserved to be in a single plane, although it can not be determined 

 to what extent tins reflects the original habit of the plant. Leaves 

 spirally arranged, thick, keeled, acute, showing a tendency to become 

 obtuse and less appressed, especially on the older twigs. 



As here delimited tins species is confined to the older Potomac, 

 although it is very similar to those forms from the Patapsco forma- 

 tion, which are described as Widdringtonites ramosus (Fontaine) 

 Berry, the latter being more copiously branched, less spreading, 

 and with more acute leaves which frequently become more or less 

 elongated. These differences may or may not be of specific value. 

 As preserved, the two plants differ decidedly in aspect, but this is due 

 largely to the spreading habit of the present species and is approached 

 in some of the coniferous twigs from Mount Vernon which are referred 

 to Widdringtonites. 



The relation to Artlirotaxis implied by the name is not certain and 

 the present species is retained in the genus to which it was referred 

 by Professor Fontaine more from a desire to avoid changes which do 

 not appear to be justified by the meager evidence at hand than from 

 any conviction of relationship. For the same reason it was not trans- 

 ferred to Widdringtonites, although it seemed desirable in the case of 

 Widdringtonites ramosus to make such a change and bring the latter 

 in association with the Upper Cretaceous species of that genus, with 

 which there is such a close agreement. 



Following Seward's suggestion, 1 the cones which Professor Fon- 

 taine referred to this species are considered to belong to Sphenolepis 

 kurriana (Dunker) Schenk, as are also some of the leafy twigs winch 

 Fontaine identified as Arthrotaxopsis, and a number of the recorded 



i Seward, Wealden Flora, pt. 2, 1895, p. 201. 



