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, 

 PI. Wright, i. 61, & Trans. Linn. Soc. xxx, 425. — Common on lime- 

 stone hills of Northern Mexico ; near Monterey, Gregg, no. 182; Saltillo, 

 WisUzenus, no. 300, Gregg; Parras, Palmer, no. 296 (coll. of 1880); 

 Carneros Pass, Pringle, uos. 2851, 3703. 



= = Pinnae 1 pair ; leaflets 2 to 4 pairs, obovate or suborbicular, 2 cm. in length. 



44. M. leucsenoides, Benth. Tall shrub or small tree, 3 to 

 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 bi-anches : 

 legume 5 to 6.5 cm. long, 4 to 8 mm. broad, unarmed. — Benth, in 

 Hook. Lond. Jour. Bot. v. 89, & Trans. Linn. Soc. xxx. 421. — 

 Zimapan, Th. Coulter, and Mexico without locality, Karwinski, ace. to 

 Hemsl. Pringle's no, 3750 collected on limestone ledges at Las Palmas, 

 San Luis Potosi, doubtless represents this species, 



= = = Pinnse 1 to oc pairs; leaflets 2 to oc pairs, oblong to elliptic, mostly small. 

 a. Branchlets, petioles, and rbachises glabrous eveu under lens. 

 1. Spines infra-stipular, geminate. 



45. M. tenuiflora, Benth. Stipules setaceous : pinnte 1 to 3 

 pairs, obliquely oblong: peduncles somewhat longer than the leaves, 

 the upper ones racemose. — Benth. in Ilook. Lond. Jour. Bot, v. 92, 

 & Trans. Linn. Soc. xxx. 429. — Zimapan, Mexico, T/i. Conlter ; Mexico 

 without further locality, Karwinski, ace. to Benth. Species not seen 

 by the writer ; the description compiled. 



2. Spines (with rare exceptions) single, borne at tlie side of tlie axil and 30° to 



120° removed from it. 



46. M. borealis, Gray. Shrub, 1,5 to 2.5 m, high: leaves small; 

 pinn?e mostly a single pair ; leaflets 3 to 5 pairs, oval, 2 to 4 ram. long, 

 two thirds as broad, thickish, glancescent : peduncles very slender, 12 to 18 

 mm. long: legumes 2.5 cm. or more long, unarmed or more often armed 

 on one or both edges ; segments about 4, rounded at the sides. — PI. 

 Fendl, 39, & PL Wright, i. 61 (excl. var.), ii. 51 ; Benth. Trans. Linn. 

 Soc. xxx. 426, t. 66. M. fragrnns. Gray, PI. Wright, ii. 51, not PI. 

 Lindh. — W, Texas, Wright, Hayes, ro. 220, Havard, no. 68 ; New 

 Mexico, Fendler, no. 181, Wright, no. 1038, northward to Cimarron 

 Valley, Indian Teri\, Carleton, ace. to Holziuger. Perhaps only a 

 variety of the next. 



47. M. fragrans, Gray. Fragrant shrub, 6 to 12 dm, or more 



