72 



THE CACTACEAE. 



The plant inhabits crevices of rocks and locally is very abundant. On Mona Island, 

 between Porto Rico and Santo Domingo in the Mona Passage, it exists in immense numbers 

 on the limestone plateau. 



Mammillaria tortolensis (Pfeiffer, Enum. Cact. ii. 1837) was published by Pfeiffer as a 

 synonym of M. nivosa. The same or similar plant was briefly described by Forbes (Journ. 

 Hort. Tour 148, 1837). 



Illustrations: Forster, Handb. Cact. ed. 2. 331. f. 34; Schelle, Handb. Kakteenk. 264. f. 

 186; De Laet, Cat. Gen. f. 46; Bliihende Kakteen 3: pi. 165, as Mammillaria nivosa. 



Figure 66 is from a photograph of a plant collected on Turks Island, British West 

 Indies, in July 191 6 and sent us by the Director of the New York Aquarium; figure 243 

 (Britton and Rose, Cactaceae 3: p. 231) shows the plant on Mona Island, Porto Rico. 



Fig. 66. — Neomammillaria nivosa. 



3. Neomanunillaria gaumeri sp. nov. 



Cespitose, the branches short, globose to short-cylindric, up to 15 cm. long, growing half 

 hidden in the sand; tubercles dark green, short, nearly terete, obtuse, 5 to 7 mm. long, very milky; 

 axils naked even when young ; spine-areoles conspicuously white-woolly at first, soon naked ; radial 

 spines 10 to 12, spreading, acicular, white with brown tips or lower ones in cluster darker, 5 to 7 mm. 

 long; central spine solitary, porrect, usually brown; flowers very abundant from near top of plant 

 but not from axils of young areoles, creamy white, small, 10 to 14 mm. long; outer perianth- segments 

 greenish, brown-tipped; scales on flower-tube broadly ovate, scarious; fruit crimson, clavate, 18 to 

 20 mm. long, naked. 



Common in the sand dunes of Progreso, Yucatan; collected first by George P. 

 Gaumer and sons, April 191 6 (No. 23349, type) ; re-collected in 1918 and again in 192 1. 



This species is remarkable for its unusual habitat and was the first of the genus reported 

 from Yucatan. A second species has since been collected by Dr. Gaumer (see p. 114). 



