54 The cactaceae). 



ing; spines 3 to 5, short (10 to 12 mm. long), spreading, covered with thin, brown, papery sheaths, 

 the lowest one stoutest; flowers 3.5 cm. broad, brownish; fruit 2 cm. to 3 cm. long, spineless; seeds 

 nearly globular, 4 mm. in diameter. 



Type locality: Bacuachi, Sonora, Mexico. 



Distribution: Western coast of Mexico. 



Opuntia thurberi has long been one of our least-known species. The type, which is 

 but a fragment, has not been clearly associated with any recent collections, but we are 

 disposed now to believe that specimens collected on the west coast of Mexico by Dr. Rose 

 in 1910 belong here. If we are correct, it ranges from Sonora to Sinaloa, Mexico. It is 

 sometimes associated with Opuutia versicolor in its northern range, but is not so stout and 

 has fewer and longer spines. 



Figure 63 is from a photograph of the type specimen. 



12. Opuntia clavellina Engelmann in Coulter, Contr. U. S. Nat. Herb. 3: 444. 1896. 



Plant I meter high or less, rather openly branched; ultimate joints slender, spreading or ascend- 

 ing, somewhat clavate, 5 to 10 cm. long, a little over i cm. in diameter; tubercles prominent, 

 elongated; spines 3 to 6 in a cluster, very long, covered with loose straw-colored or brown sheaths, 

 the central one much longer and porrect; flowers yellow; fruit clavate, short, tuberculate. 



Type locality: Near Mision Purisima, Lower California. 



Distribution: Interior of central Lower California. 



The above description is based on the original one and on the t3^pe If the plant illus- 

 trated as cited below belongs here, this is a very distinct species, which was referred, however, 

 by Mrs. Brandegee to Opuntia molesta Brandegee. 



Illustration: Contr. U. S. Nat. Herb. 16: pi. 129, a. 



Of this series there is another peculiar Lower California species, perhaps nearest 0. 

 clavellina, but of different habit and spines. It also suggests 0. tetracantha of Arizona. 

 It was obtained first by Dr. Rose in 191 1, but was without flowers or fruit. It may be 

 characterized as follows : 



Opuntia sp. 



Stems slender (i to 1.5 cm. in diameter), weak, often clambering over bushes, pale green in 

 color, terete, pointed, 6 to 7 dm. long; areoles set on low tubercles, circular; chief spines 2 to 6, 

 only slightly spreading, nearly equal, 1.5 to 2.5 cm. long, clothed with loose straw-colored sheaths 

 (rose-colored when very young) ; accessory spines 3 or 4, almost bristle-like, borne from the lower 

 parts of the areoles; glochids short, greenish when young, yellow in age; flowers and fruit not seen. 



Collected by Dr. J. N. Rose on Cerralvo Island, off southern Lower California, April 19, 

 191 1 (No. 16875), ^i^d also by Nelson and Goldman on the same island in 1906 (No. 7524). 



13. Opuntia davisii Engelmann and Bigelow, Proc. Amer. Acad. 3: 305. 1856. 



Plants low, 3 to 5 dm. high, much branched, their dense covering of straw-colored spines making 

 them conspicuous objects in the landscape; terminal joints slender, 6 to 8 cm. long, about i cm. in 

 diameter, strongly tuberculate; spines 6 to 12, unequal, the longest ones 4 to 5 cm. long, acicular, 

 covered with thin sheaths; glochids numerous, j'ellow; flowers, including ovary, 3.5 cm. long; petals 

 olive-green to yellow, broad, with rounded mucronate tips; ovary with large areoles bearing a few 

 spines each; fruit 3 cm. long, somewhat tuberculate, naked; seeds not known. 



Type locality: Upper Canadian, about Tucumcari Hills, near the Llano Bstacado. 



Distribution: Western Texas and eastern New Mexico. 



For many years this plant was not collected and the name was confused with other 

 species, so that at one time it was supposed to extend as far west as California. It is now 

 believed to have a rather circumscribed range. It is first seen going west on the Texas & 

 Pacific Railroad about Colorado, Texas. 



The plant was named for Jefferson Davis, who was Secretary of War when Whipple's 

 report was made. 



