no.1769. FOSSIL PLANTS OF Till' POTOMAC GROUP BERRY. 629 



ACROSTICHOPTERIS ADIANTIFOLIA (Fontaine i. 



Baieropsis adiantifolia Fontaine, Monogr. I'. S. Geol. Surv., No. 15, L890, p. 211 

 pi. 92, figs. 8, 9; pi. 93, figs. I 3; pi. 94, figs.2,3. Fontaine, in Ward, 19th 

 Ann. Rept. I". S. Geol. Surv., 1899, pt. 2, p. 684, pi. L68, fig. 8. Fontaine, 

 in Ward, Monogr. I. S. Geol. Surv., No. 4S, 1905, pp. 510, 528, 538. 



Description -The original description by Fontaine in 1890 is as 



follows: 



Stems moderately strong; leaves subopposite to opposite, closely placed, often 

 imbricated, subquadrilateral to flabellate fan-shaped, narrowed to a wedge-shaped 

 base, and attached by a shorl pedicel which springs from the lower corner of the leaf 



Bo that the inner margin of the leaves runs close to the main stem, parallel with it, and 

 often overlapping it, while the lower margin of the leaves stands nearly at right angles 

 with the main stem; leaves cut down to near the base into two principal lacinise, and 

 those higher cut into two or more minor laciniae; ultimate laciniae very shallow and 

 strap-shaped, ending in acute very short teeth, or rarely in narrowly elliptical and 

 subacute ones; all the lacinige turned outwards or upwards, the lower margins of the 

 leaves being entire or having sometimes an acute tooth; leaves in ascending towards 

 the tips of the leafy branches have their lower margins directed more and more up- 

 wards, become smaller, assume more of an elliptical or a wedge shape, have the 

 laciniae only on the upper margin, an,! finally coalesce to form a terminal leaflet, 

 which at base shows three segments, hut whose terminal portions are not seen; nerves 

 fine hut distinct, branching at base from a mother nerve and then dividing repeatedly 

 in a dichotomous manner so as to fill the laminae, and have the branches ending in the 

 teeth. 



The plant is mosl frequent at Fredericksburg but is not abundant there, and is 

 usually in a very fragmentary state. If we look to the shape of the leaves alone this 



curious plant is much like a fern of the t\| f Adiantum, but the gradations through 



different forms connect the specimens so closely with the flabellate leaves of Baieropsis 

 that they can not be separated by any good distinctions. The principal difference 

 from the more common and typical forms of Baieropsis is found in the greater pro- 

 portional width of the leaves and the smaller depth of file subdivision. 



This species is based upon very fragmentary specimens and it is 

 very doubtful if the material identified from the Patapsco and 

 Arundel formations is the 1 same as that from the Patuxent, the pres- 

 ence of this species from Chinkapin Hollow, Virginia, and Arlington 

 and Fort Foote, Maryland, being each based on a single very poor 

 specimen. 



Occurrence.- Lakota formation. Barrett and Hay Creek, Wyo- 

 ming. Patuxent formation. Fredericksburg, Potomac Run, Tele- 

 graph Station, Virginia. Patapsco formation. Fort Foote, (?) 

 Maryland and Chinkapin Hollow, ('.), Virginia. Arundel forma- 

 tion. Arlington, ( '.) Maryland. 



Collections. V. S. National Museum. 



