DESCRIPTIONS OF SPECIES. 91 



Order NYMPH^EACEiE. 



Cabomba (!) gracilis, Newb. 



PI. XXII, fig. 1; XXIII, fig. 1. 

 Cdbomba gracilis Newb. Proc. U. S. Nat. Mus., Vol. V (March 21, 1883), p. 514. 

 Ills. Cret. and Tert. PL (1878), PI. VII, fig. 1, under "aquatic rootlets of 

 Equisetuin"; VIII, fig. 2, under " Equisetum." 



"Stern slender, smooth; submerged leaves set at intervals of half an 

 inch to an inch apart on the stem, opposite dichotomously and frequently 

 branched, segments narrowly linear, or filiform, flattened, smooth, trun- 

 cated, scarcely distinguishable from the stem and leaves of C. Caroliniana." 



A large number of intertwining, smooth, narrow stems, with opposite, 

 many-forked, linear leaves, are contained in some of the collections made 

 from the Tertiary beds of the upper Missouri by Dr. F. V. Hayden. They 

 were at first regarded as aquatic rootlets, but an examination of a multi- 

 tude of well-preserved specimens shows that they are leaves and not roots, 

 and comparing them with living plants they are found to imitate with a 

 most perfect exactness the stems of leaves of Cabomba. The smaller speci- 

 mens, like that figured, accurately represent the filiform variety of Cabomba 

 Caroliniana of our Southern States. Mingled with these stems and leaves 

 are obscure fragments of what may have been the peltate leaves, since 

 some of them show a sort of umbilicus as though the point of attachment 

 of the stem. Had there been but one or two of these specimens corre- 

 sponding to the above description, their nature would have been left in so 

 much doubt as to render it unwise to call attention to them; but occurring 

 as they do in connection with other aquatic plants in very large numbers, 

 and having a definite and invariable character, the stems smooth and 

 lacking all the characteristics of creeping root stalks or aquatic roots, 

 the leaves expanded, each pair in its own plane, and the pairs alternating, 

 show that we have here to do with the stem and foliage of an aquatic 

 plant of a marked and peculiar character. To this character no living 

 plant seems to approach so nearly as Cabomba, and here the resemblance 

 is so close that the probabilities become very strong that the reference 

 to that genus will be confirmed hereafter by the discovery of the floating- 

 leaves and flowers. 



Formation and locality: Tertiary (Fort Union group). Fort Union, 

 Dakota 



