326 PROCEEDINGS OF THE AMERICAN ACADEMY. 



perhaps confluent with this species are the plants referred by Dr. Gray 

 to his M. borealis var. ? Texana, PI. Wright, i. 61 {Wright no. 159, 

 also no. 10, coll. of 1851, and Gregg, no. 51). They differ from M. 

 borealis in their puberulent rhachises and subaxillary spines, but are to 

 a certain extent intermediate between M. depauperata on the one hand 

 and M. acanthocarpa and M. hiuncifera on the other. Without better 

 and more copious material their affinities and proper status cannot be 

 more exactly determined. 



50. M. Pringlei, Wats. Branching shrub armed with mostly 

 geminate infra-stipular spines: pinnge 1 to 2 pairs; leaflets 2 to 4 pairs, 

 elliptical or oval, pale green : flowers canescent-puberulent ; bracts 

 inconspicuous: pods glabrous, 2 cm. long, acute, slightly armed on one 

 edge or unarmed. — Proc. Am. Acad. xxi. 452. — Near Big Canon of 

 the Rio Grande, W. Texas, Havnrd, no. 12, and on rocky hills near 

 town of Chihuahua, Pringle, in fruit, October, no. 545, and in flower, 

 August, no. 724. 



° ° Pinnfe (at least on well developed leaves) 3 to cc pairs ; leaflets mostly numerous. 

 + Pods 7 to 10 mm. broad, mostly obtuse or obtusish. 



52. M. Grahami, Gray. Stem nearly glabrous : primary rha- 

 chises (nearly 1 dm. in length) sparingly pubescent; pinnge about 10 

 pairs; leaflets 15 to 20 pairs narrowly oblong, of firm texture, paler and 

 prominently veined beneath, entirely glabrous upon both surfaces, usually 

 devoid even of ciliation : pods glabrous at maturity. — PI. Wright, ii. 

 52. — Mountain valleys of Northern Sonora, near the Arizonau bound- 

 ary, Wright, no. 1042. 



53. M. Lemmoni, Gray. Apparently an undershrub, covered 

 with soft and canescent pubescence or tomentum : pinnae about 6 pairs ; 

 primary rhachis 6 to 10 cm. long; secondary rhachises often 4 cm. 

 in length ; leaflets elliptic-oblong, pubescent-tomentose, 5 to 7 mm. in 

 length : heads numerous, globular, borne on filiform geminate peduncles 

 which are sometimes grouped in showy compound racemes : pods even 

 at maturity canescent-tomentose. — Proc. Am. Acad. xix. 76. — Hua- 

 chuca Mountains, Arizona, Lemmon, nos. 2692, 2693, Pringle, no. 7, 

 Tourney, no. 39. Too near the next, from which it differs chiefly in its 

 smaller spines, less woody stems, and larger less crowded leaflets. 



54. M. acanthocarpa, Benth. Stems and branches decidedly 

 ligneous : spines mostly numerous, slender or stout, usually paired and 

 infra-stipular, with or without a third one beneath the leaf-insertion ; 

 scattered spines sometimes present also : leaves (except on young and 



