DESOEIPTION OF SPECIES— AEOIDB^. 105 



to those of the other leaves. As for the small specimen (fig. 5), it is scarcely 

 possible to doubt its identity with this species; it is evidently a young leaf, 

 the nervation is, as also its shape, of the same character. All these leaves 

 are membranaceous except the middle inflated part, and in all, the veins are 

 distinct, as if the substance of the leaves was transparent. The radicles, 

 coming out in bundles from linear rootlets, confirm the reference of this spe- 

 cies to Pistia, for P. spathulata has long flexuous rootlets of the same kind, 

 with capillary radicles, often forming a coating on tlie surface of the water, 

 and seemingly supporting the plants. Comparing these plants in any of their 

 forms, none of them can be considered as representing species of Lemna, 

 not oidy on account of their size, which, even in the smaller specimen (fig. 5), 

 is greater than in any species of Lemna known at our time, but especially 

 on account of the position of the radicles, which, in Lemna, are neither 

 pediceled nor attached to the borders. This observation is applicable 

 equally well to the plants considered as Lemna by Prof Dawson. 



No species of Pistia has been published to this time from fossil speci- 

 mens. Count Saporta has recently found, in the Upper Cretaceous of Fuveau, 

 France, leaves of tliis kind {Pistia Mazelii, Sap., ined.), a species which, as 

 seen from the figures kindly communicated, has not any relation to ours. 



Habitat. — Point of Rocks, often covering large pieces of shale by 

 numerous leaves and radicular filaments. Both Dr. F. V. Haydenh and Mr. 

 Wm. Clthuni's collections have a large number of specimens representing 

 this species only. 



AROIDE^. 



ACORUS, Linn. 

 Acorus bracliystachys, Heer. 



Plato XIV, Figs. 12-15. 



Acornn bratihysiachys, Heer, Spitzb. Mioc. Flor., p. 5), pi. viii, figs. 7,8. — Lesqx., Annual Report, 1871, p. 



288 ; 1872, p. 385. 



Scape round, narrow, striate lengthwise, distantly articulate; flowering ears oblique, small, 

 oblong ; flowers numerous, in spiral around the axis. 



The scapes, four to seven millimeters thick and more or less distinctly 

 lineate lengthwise, distantly articulate, bear small flowering racemes, either 

 oblique or drooping, as in fig. 12, short, about one centimeter long and three to 

 five millimeters thick. Our fragments, as represented especially in figs. 12 

 and 13, are so exactly similar to those described and figured by Heer (loc. cit.) 



