Maryland Geological Survey 311 



in length, with ovate or lanceolate teeth with short, acute tips which may 

 be somewhat obtuse in some specimens. Tubers abundant, two or more 

 in number at the nodes, in shape oval, somewhat constricted at points of 

 attachment, as preserved about 7 mm. by 8 mm. in diameter. 



The preservation of all of the Potomac specimens is poor, and the 

 great majority are partially or wholly decorticated and otherwise much 

 macerated, indicating prolonged submergence before fossilization. In 

 neither of the specific forms established by Fontaine are there any con- 

 stant characters which serve to distinglish them from the widespread 

 Equisetum Burchardti of Europe, with which they are here identified. 

 This species was described by Dunker from the Wealden of Hanover, 

 along with its tubers in various stages of preservation. These he failed to 

 recognize as such, describing them as various species of Carpolithus. 

 Schenk in 1871 gave a much better diagnosis of this species and also 

 pointed out the true nature of Dunker's various species of Carpolithus. 



The species is common in the Wealden of England and has been re- 

 corded from the Barremian of Austria, the Valanginian or Lower Neo- 

 comian of Portugal, and the Lakota formation in the Hay Creek coal 

 field of Wyoming. Equisetum usliimarense Yokoyama ^ from Japan is 

 a closely allied if not identical form. 



Occurrence. — Patuxent Formation. Terra Cotta (obscure rhizome) 

 and ISTew Eeservoir (common). District of Columbia; Dutch Gap, Cock- 

 pit Point, Telegraph Station (Lorton), Virginia. Patapsco Forma- 

 tion, Federal Hill (Baltimore), Maryland. 



Collection. — TJ. S. National Museum. 



Equisetum Lyelli Mantell 

 Plate XLI, Figs, 7, 8 



Equisetum Lyelli Mantell, 1833, Geol. S. E. England, p. 217, fig. 52, 1-3 on 



p. 245. 

 Eguisetites Lyelli Bronn, 1848, Index Pal., p. 464. 

 Equisetum Lyelli Brongniart, 1849, Tableau, p. 107. 

 Equisetum Lyelli Goppert, 1849, in Bronn, Geschichte der Natur, Band lii, 



p. 13. 

 Eguisetites Lyelli Unger, 1850, Gen. et Sp., p. 60. 

 Equisetites Lyelli Morris, 1854, Brit. Foss., p. 8. 



^ Journ. Imp. Univ. Tokyo, vol. iii, 1890, p. 39, pi. xi, figs. 1-3. 



