142 DESCRIPTION OF SPECIES. 



present epoch have a wide range of distribution; the two species ( T. lati- 

 folia and T. an gusti folia) are as common on the North American continent 

 as I hey are in Europe. 



Hah. — Florissant; Randolph County. U. S. Geol. Expl. Dr. Hayden. 



POTAMOGETON, Linn. 



Potamogeton ? verticillatus, sp. nov. 



Plate XXIII, Figs. 5, G. 



Stems slender; leaves verticillate or tufted, grass-like, linear-lanceolate, largest 

 toward the base, sessile and narrowed to the point of attachment, nerved lengthwise 

 in the middle; branches very slender, floating or pendant, bearing tufts of shorter 

 leaves. 



This species differs from its congeners by the position of the leaves 

 in verticils upon apparently articulate stems. It is distantly related to 

 P. ccespitans, Sap., "Et.," i, p. 76, pi. iv. fig. 2. 



Hah. — Florissant. The specimen (fig. 5) is from the Explor. of Dr. 

 F. V. Hayden; the other belongs to the Princeton Museum. 



Potamogetoii geniculatus, Al. Br. 



"Stizenb. Verz.," p. 75; Heer, "Fl. Tert. Helv.," i, p. Wi, pi. xlrii, figs. 1-G; Ett., - Fl. v. Biliu," p. -29, pi. vii, 

 figs. 1,2. 



Stems slender, branching, geniculate-flexuous; leaves narrowly linear, acuminate, 

 fasciculate, sessile; fruits round or broadly oval-apiculate, 1 millimeter in diameter. 



Though the specimens merely represent the upper part of a stem the 

 characters of the leaves and the fructification refer the plant to Heer's 

 species. The fruits are slightly smaller, however, rather round than ovate 

 or exactly like those represented by the author, pi. xlvii, fig. be. 



Hab. — Florissant. No. 69 of Lacoe Collection. 



NAJADOPSIS, Heer. 

 Najadopsis rugulosa, sp. nov. 



Plate XXIII, Fig. 7. 



Stem dichotomous from inflated apicial innovations; segments flat, dichotomous, 

 linear, acuminate, decurrent to the main stem; surface merely irregular and minutely 

 wrinkled lengthwise, without trace of medial nerves. 



The substance of this plant is somewhat thick; the leaves or segments 



seem to have been originally cylindrical, though quite flat upon the stone, 



by compression? All that can be seen of the plant is figured. It has an 



