150 



Descriptions of some new Grasses. 



Corolla two-valved ; inferior valve ovate-lanceolate, 

 toothed at the apex, three-nerved ; superior valve sub-bicari- 

 nate, two-nerved, 2 — 4-toothed at the tip. 

 Stamens three ; anthers linear, yellow. 

 Hab. On the high plains of the Trap Formation at the sources 

 of the Canadian River. July. 



This genus resembles, in many respects, the jEgopogon of 

 Humboldt and Bonpland, but is still very distinct. In the 

 latter, the spikelets are pedicellate and similar in structure ; 

 the only difference being that of sex : while in the Pleuraphis 

 they are sessile, and the central spikelet different from the rest. 

 The ./Egopogon is also destitute of a villous involucrum, which 

 is very conspicuous in the Pleuraphis. One of the most remark- 

 able characters of our new genus (from which the name is de- 

 rived) is to be found in the calyx of the lateral spikelets, one 

 of the glumes of which is armed with a pretty long bristle 

 proceeding from its side, a circumstance which I have not ob- 

 served in any other grass. In the elaborate Agrostographia of 

 P. de Beauvois there is no genus to which I can refer this grass, 

 nor is it to be found in the more recent work of Trinius, on 

 the Gramina. 



Explanation of the plate. . 



Fig . 1 . A plant of the natural 

 size. 



2. A congeries of spikelets. 



3. The same separated. 



4. A lateral spikelet. 



5. The same magnified. 

 6-7. Glumes of the same. 

 8. Corolla. 



0. Inferior valve of the 



same. 

 !0. Stamens. 



Fig. 11. Central spikelet. 

 12. The same magnified. 

 13-1 4. Glumes of the same 



15. Corolla. 



16. Inferior valve of the 



same. 



17. Superior valve. 



18. Stamens. 



19. Germen, styles, and 



stigmas. 



20. Nectaries. 



