no. 1821. REVISION OF POTOMAC PLANTS— BERRY. 295 



bridge, Virginia. Arundel formation : Langdon, District of Colum- 

 bia; Hanover, Tip Top, Soper Hall, Maryland. Patapsco forma- 

 tion: Grays Hill, Fort Foote, Stump Neck, Maryland; Mount Ver- 

 non, White House Bluff, Hell Hole, Chinkapin Hollow, 72-mile post, 

 Dumfries Landing, near Widewater, Aquia Creek, Virginia. 



Collections. — U. S. National Museum, Johns Hopkins University. 



THE GENUS ARTHROTAXOPSIS OF FONTAINE. 



The genus Arthrotaxopsis was named from its resemblance to the 

 modern genus ArtJtrotaxis Don, of the subfamily Taxodiea?, which has 

 three species confined to Tasmania. 



Artlirotaxopsis is characterized in the following terms by its 

 describer: x 



Trees or shrubs, copiously branching, with principal stems or branches proportion- 

 ally strong, cylindrical, rigid, sending off thickly placed, long, slender, cord-like, 

 ultimate twigs, all in the same plane and spreading widely; the ultimate twigs leave 

 the penultimate ones under a very acute angle and show a tendency to a fastigiate 

 grouping; cones mostly broadly oblong, rarely globular, obtuse and rounded at base 

 and apex, average dimensions 10 mm. by 14 mm., attached singly on the summit of 

 short lateral branches and placed on the lower portions of the leafy stems and branches, 

 the twig with its cone representing the branching leafy twigs which occur higher up; 

 scales of the cones woody, thick, wedge-shaped in the basal portions, expanded at the 

 free ends, and probably shield-shaped, numerous, spirally placed, attached at a large 

 angle, the middle pnes being nearly or quite at a right angle with the axis, close ap- 

 pressed, opening with age; seed under each scale one, elliptical in shape, smooth and 

 bony in texture, average dimensions 1 mm. by 2.5 mm. ; leafy branches ending abruptly 

 in an ultimate twig similar to those sent off pinnately and alternately lower down; 

 leaves very thin and scale-like, elliptical, rhombic, or oblong, with varying age chang- 

 ing their shape, the rhombic forms representing the oldest and most crowded leaves, 

 slightly keeled on the back, spirally arranged. 



The only qualification that it is necessary to make in the foregoing 

 description is that referring to a single, smooth, bony seed under each 

 cone-scale. The present writer has been entirely unable to verify 

 this feature in any of -the material. The cones are of small size and 

 comparable to the cones usually referred to Sequoia — i. e., with 

 wedge-shaped, peltate scales. The material is all poorly preserved 

 and the leafy twigs have evidently •suffered greatly from decay before 

 fossilization. 



The genus may be distinguished from Arthrotaxites Unger, 2 Ech- 

 inostrobus Schimper, 3 and Cyparissidium Heer, 4 all of which have 

 very similar leafy twigs, by the characters of the cone, which are quite 

 different. The first two are Jurassic, while the last extends from the 

 Rhaetic to the Upper Cretaceous. As a rule the twigs of Arthro- 

 taxopsis are more elongated and slender than those of these other 

 genera, indicating in all probability a pendulous habit. 



i Fontaine, Monogr. U. S. Geo! Surv., vol. 15, 1890, p. 239. 



2 Unger, Bot. Zeit., 1849, No. 19. 



a Schimper, Pal. Veget, vol. 2, 1870, p. 330. 



<Heer, Flora Foss, Arct., vol. S, pt. 2, 1874, p. 74. 



