﻿Evans: The genus Plagiochasma 295 



thallus about one fourth the width; epidermis composed of thin- 

 walled cells with distinct trigones often having bulging sides and 

 a thin cuticle with a waxy covering, the cells averaging about 22 n 

 in diameter; pores slightly elevated, rather small, surrounded by 

 about six (five to eight) radiating series of cells with two or three 

 cells in each series, radial walls distinctly (and sometimes strongly) 

 thickened ; aeriferous layer about three fourths the thickness of 

 the thallus, of a rather loose structure, the air spaces about twice 

 as wide as the green cells; ventral scales lunulate, purple, slightly 

 overlapping, irregularly sinuous-dentate along the margin with 

 somewhat contorted cells, bearing evanescent slime-papillae, cells 

 containing oil bodies few and scattered, the scales abruptly 

 contracted into one or two ovate-lanceolate appendages, obtuse 

 to acute at the apex, entire, more or less constricted and plicate at 

 the base: inflorescence monoicous (autoicous): cf inflorescence 

 borne behind the 9 receptacle or on a short ventral branch: 

 9 receptacles borne singly or in a median row of two or three; 

 peduncle mostly 1.5-2 mm. long (3-4 mm. long, according to 

 Stephani); carpocephalum narrowly concave at the apex, two- 

 or three-lobed with apiculate lobes, maturing two or three sporo- 

 phytes; scales of carpocephalum linear-lanceolate, acuminate, 

 entire; spores brownish yellow, 75-85 /t in diameter, minutely 

 rugulose, regularly reticulate, spherical face usually with twelve or 

 thirteen meshes, plane faces each with four meshes, reticulum often 

 incomplete ; elaters gradually attenuate, mostly 225-250 /x in length 

 and 7-9// in maximum diameter, spirals two or three, often 

 somewhat coalescent. [Fig. 6.] 



The following specimens have been examined : 



Texas: under overhanging rocks along steams, San Marco, 

 1848, C. Wright g (type). 



Arizona: Nogales, February, 1902, D. T. MacDougal. 



Coahuila: San Lorenzo Canyon, about 3.5 km. southeast of 

 Saltillo, September, 1904, E. Palmer 423. 



Durango: near the city of Durango, 1896, E. Palmer 862. 



Vera Cruz: Cordova, without date, C. Salle; Orizaba, Feb- 

 ruary, 1885, W. G. Farlow 17 (in Farlow herbarium). 



No other localities have been reported. 



In studying the present species the writer has had the privilege 

 of examining a portion of the type material. Although carpo- 

 cephala and sporophytes are present, the spores and elaters are 

 poorly or abnormally developed so that it is impossible to gain from 

 them an accurate idea of the typical structure of these organs. 



