68 PROCEEDINGS OF THE AMERICAN ACADEMY. 
lower surfaces; margins entire or closely serrulate, slightly revolute, with 
5 to 9 pairs of sete mostly below the middle: heads solitary or in small 
terminal or axillary clusters : involucre oblong, 5 to 7 mm. high, 3 or 4 
mm. broad, 9-25-flowered ; bracts 5, oblong, blunt, with scarious margins 
and prominent thickened keels: pales sparingly serrulate, 2 to 2} mm. 
long: akenes spreading-hirsute or glabrate, 834 to 4 mm. long. — Ie. iv. 
12. t. 824; Less. Linnwa, vi. 714; DC. Prodr. v. 100. Chthonia pros 
trata, Cass. Dict. Sci. Nat. ix. 173. — A common and polymorphous 
species, the typical form growing from the Southwestern United States 
to Yucatan and Guatemala. Arizona, near Camp Grant (Rothrock, 
no. 722), sandy plains near Mexican boundary (Pringle); New Mexico 
(C. Wright, nos. 245, 1123) ; Sonora (Thurber, no. 971), Alamos 
(Palmer, 1890, no. 659) ; Durango (Palmer, 1896, no. 512) ; San Luis 
Poros (Parry & Palmer, no. 861); Oaxaca (Nelson, no. 1693); 
Yucatan (Schott, no. 533, Gaumer, nos. 788, 1092); GUATEMALA, 
Santa Rosa (Heyde & Lux in John Donnell Smith’s Exsic., no. 3366"), 
Canchén (Heyde & Lux, no. 6154). A puzzling form with narrow 
heads and leaves setiferous to the tip has been collected in Guatemala 
(Heyde & Lux, no. 4232). 
Var. cylindrica. Leaves generally rounded at the tips, rarely 
mucronate ; setz fewer, 2 to 5 pairs near the base: heads generally soli- 
tary (in one specimen clustered): involucre longer and narrower, 8 ¢ 
9 mm. high, 2 or 3 mm. broad; bracts 3, thin, plane or a little condupl 
cate, finely canaliculate, the mid-vein slightly or scarcely thickened into 
a keel: akene and pappus a third longer than in the type. — Southwest- 
ern United States and adjacent Mexico. Arizona (Palmer, 1867, 
no. 128), Apache Pass (Lemmon, no. 619); New Mexico (Palmer) 5 
(Palmer, 1887, no. 145). 
Var. urceolata. Ferruginous-pubescent on the stems, midribs, and 
involucres: leaves large, the larger 35 cm. long, 6 mm. wide, with 8 
12 pairs of sete: involucre urceolate, 9 or 10 mm. high; 
bracts with broad rounded pubescent keels. — CHIHUAHUA, Ha 
San José (Palmer, 1885, no. 53). 
cienda 
== = Pappus a row of linear-attenuate setulose pales, with a minute exterior sett 
lose crown at the base; pales the same number both in the disk and in the ray> 
P. Schaffneri, Schz. Bip. Very low and slender, 5 cm. or 80 “ 7 
m. JODE; 9 
entire: 
stems puberulent: leaves linear-attenuate, cuspidate, 1} to 2} ¢ 
1 to 13 mm. wide, margins entire or minutely serrulate, becoming 
Coanuita, Monclova (Palmer, 1880, no. 640); Sonora, Guaymas © 
the 5 thick 
