324 PROCEEDINGS OF THE AMERICAN ACADEMY. 
small leaflets obovate or suborbicular, 2 to 4 mm. in diameter: pods 
unarmed or rarely bearing a few marginal spines.— Benth. in Gray, 
Pl. Wright. i. 61, & Trans. Linn. Soc. xxx. 425.— Common on lime- 
stone hills of Northern Mexico; near Monterey, Gregg, no. 182; Saltillo, 
Wislizenus, no. 3800, Gregg; Parras, Palmer, no. 296 (coll. of 1880); 
Carneros Pass, Pringle, nos. 2851, 3703. 
= = Pinne 1 pair; leaflets 2 to 4 pairs, obovate or suborbicular, 2 cm. in length. 
yp 44. M. leuczenoides, Benrn. Tall shrub or small tree, 3 to 
A 
4.5 m. in height, unarmed: petioles rather short (1 cm. in “length): 
leaflets at first puberulent, later glabrate, lucid, subcoriaceous, veiny : 
heads axillary, racemose and subcorymbose at the ends of the branches: 
Zimapan, 7h. Coulter, and Mexico without locality, Karwinski, acc. to 
Hemsl. Pringle’s no. 3750 collected on limestone ledges at Las Palmas, 
San Luis Potosi, doubtless represents this species. 
= = = Pinne 1 to « pairs; leaflets 2 to o pairs, oblong to elliptic, mostly small. 
a. Branchlets, petioles, and rhachises glabrous even under lens. 
1. Spines infra-stipular, geminate. 
45. M. tenuiflora, Benru. Stipules setaceous: pinne 1 to 3 
pairs, obliquely oblong: peduncles somewhat longer than the leaves, 
the upper ones racemose. — Benth. in Hook. Lond. Jour. Bot. v- 92, 
& Trans. Linn. Soc. xxx. 429. — Zimapan, Mexico, 7h. Coulter ; Mexico 
without further locality, Karwinski, acc. to Benth. Species not seen 
by the writer; the description compiled. 
2. Spines (with rare exceptions) single, borne at the side of the axil and 30° to 
120° removed froin it. 
46. M. borealis, Gray. Shrub, 1.5 to 2.5 m. high: leaves small ; 
pinnz mostly a single pair; leaflets 8 to 5 pairs, oval, 2 to 4 mm. long; 
two thirds as broad, thickish, glaucescent: peduncles very slender, 12 to 18 
mm. long: legumes 2.5 em. or more long, unarmed or more often armed 
on one or both edges; segments about 4, rounded at the sides. ae 
Fendl. 39, & Pl. Wright, i. 61 (excl. var.), ii. 51; Benth. Trans. Linn. 
Soc. xxx. 426, t. 66. M. fragrans, Gray, Pl. Wright, ii. 51, not Pl 
Lindh. — W. Texas, Wright, Hayes, ro. 220, Havard, no. 68; New 
Mexico, Fendler, no. 181, Wright, no. 1038, northward to Cimarron 
es Valley, Indian Terr., Carleton, acc. to Holzinger. Perhaps only 
47. M. fragrans, Gray. Fragrant shrub, 6 to 12 dm. or more 
