172 Proceedings of the Biological Society of Washington. 



ratures: larger sporophylls (seta included) 1.7 to 2.3 mm. long, averaging 

 0.9 mm. broad. Megasporangia few, basal and mostly ventral; megas- 

 pores about 0.45 mm. in diameter, yellow, delicately reticulate, the narrow 

 low ridges and the broad surfaces of the areoles smooth; microspores 

 bright yellow to orange, up to 0.055 mm. in diameter, granulose. 



Type in the United States National Herbarium, no. 48,133, collected 

 on Quanah Mountain, Oklahoma, July 28, 1891, by C. S. Sheldon (no. 233) ; 

 originally listed* as S. rnpestris (L.) Spring. 



The following additional specimens of £. Sheldoni are in the National 

 Herbarium : 



Oklahoma: Headquarters Mountain, near Granite, on barren granite, 

 May 4, 1918, F. C. Greene; Chickasha, on sandstone, June 10, 1918, F. C. 

 Greene. 



Texas: Crab Apple Creek, Gillespie County, G. Jermy 313; Murphys- 

 ville, July, 18S3, V. Havard; Alpine, Brewster County, March 7, 1918, 

 E. O. Wooton. 



Of the species known from the United States Selaginella Sheldoni 

 might be confused only with S. Wrightii, of the Mexican Border region, 

 which it resembles in its prostrate habit and recurved sterile branchlets. 

 The resemblance is only superficial, however, S. Wrightii differing in all 

 essential characters. The stems of the latter are shorter; the leaves are 

 chartaceous, decidedly greener, and much longer (up to 3.5 mm. long), 

 have the attenuate apex tipped by a short, stiff, lutescent seta, and bear 

 longer and more numerous cilia; the spikes are about twice as long as 

 those of S. Sheldoni; the sporophylls are narrower and longer and bear 

 a shorter seta and more numerous cilia; and the megaspores are not only 

 one-third smaller but strongly flexuose-rugulose, in marked contrast to 

 the delicately reticulate megaspores of S. Sheldoni. In megaspore and other 

 characters S. Sheldoni is related, apparently, to a small subgroup of Mexi- 

 can species, several of which are undescribed. 



• Contr. U. S. Nat. Herb. 1 : 201. 1892. 



