464 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Spikelets scattered in a flexuous spike : scales 

 lanceolate : perigynia orbicular, abruptly slen- 

 der-beaked (12) C. tenera, var. Richii. 



□ □ Scales blunt or at most acutish. 



Spikelets gray-green or finally dull brown, with 

 strongly appressed-ascending very firm perigynia 

 3.5 to 4 (very rarely 4.5) mm. long 



(9) C. alboluteseens. 

 Spikelets straw-colored or ferrugineous, with spread- 

 ing-ascending perigynia 4 to 5.5 mm. long. 

 Spike of 5 to 10 mostly distinct spikelets 



(16) C.festucacea. 

 Spike of 3 to 6 approximate spikelets 



(16) C.festucacea, var. brevior. 

 2. Tips of perigynia equalled by the subtending scales. 



O Spike stiff and erect, or at least with approximate spikelets. 

 + Spike whitish or gray-green. 

 X Perigynia lance-ovate, 4 to 4.8 mm. long, nerveless on the 



inner faces, golden-yellow at base . . (20) C. xerantica. 

 X X Perigynia broad-ovate to suborbicular. 



Perigynia strongly ribbed the length of the inner faces, 



2 mm. broad (18) C.foenea. 



Perigynia nerveless or faintly nerved on the inner faces, 



broader (9) C. alboluteseens. 



+ + Spike bronze or ferrugineous. 



Perigynia distinctly concave on the usually nerved inner 



faces: achene 1 mm. broad (19) C. leporina. 



Perigynia flat or convex on the usually nerveless inner 

 faces, very plump: achene 2 mm. broad . (22) C. adusta. 

 O O Spike flexuous, at least the lowest spikelets remote. 



+ Perigynia nerveless or only faintly short-nerved on the inner 

 faces. 

 Perigynia ovate-lanceolate, one-third as broad as long : 



achene 1 mm. broad (7) C.praticola. 



Perigynia ovate, half as broad as long : achene 1.5 mm. 



broad (21) C. aenea. 



+ + Perigynia distinctly nerved on the inner faces. 



X Perigynia 2.8 to 4.4 mm. long, at most 2.4 mm. broad, 7- to 

 13-ribbed on the inner faces, abruptly beaked. 

 Spike of 4 to 9 spikelets 6 to 10 mm. long : perigynia 2.8 



to 4 mm. long (18) C.foenea. 



Spike of 6 to 15 spikelets 10 to 17 mm. long: perigynia 

 3.5 to 4.4 mm. long . . . (18) C.foenea, var. perplexa. 

 X X Perigynia 4 to 5.3 mm. long, 2.5 to 3 mm. broad, 3- to 5- 

 nerved on the inner faces, obscurely broad-beaked 



(14) C. silicea. 

 ** ++ Bracts leaf-like and much prolonged, the lowest 1 to 2 dm. long : 



spikelets crowded : perigynia subulate .... (23) C. sychnocephala. 



