﻿Evans: The < 



Plagiochasma 



in which a uniform thickening has never been observed, so that 

 it is allowable to associate this peculiarity with certain species, 

 even if they may sometimes develop elaters of the usual type. 



Description of the North American species 

 The seven North American species with their known ranges, 

 according to published records, are the following: P. crenulatum, 

 Mexico; P. elongatum, Mexico and China; Aytonia Evansii, 

 Jamaica; P. intermedium, Mexico and Guatemala; Aytonia 

 jamaicensis, Jamaica; P. mexicanum, Mexico; and P. Wrightii, 

 Texas. In the writer's opinion, however, P. elongatum, Aytonia 

 Evansii, and P. mexicanum represent synonyms of the widely 

 distributed P. rupestre. This reduction to synonymy would 

 diminish the total number of North American species to live, if 

 it were not for a Mexican species proposed as new, which raises 

 the number to six. In certain cases it has proved possible to 

 extend the known ranges of individual species to a considerable 

 extent. The six species recognized in the present paper may be 

 distinguished as follows: 



Key t 



Epidermal pores o 



, usually surround* 



Appendages of ventr 





I. Plagiochasma rupestre (Forst 

 rupestris Forst. Char. Gen. Plant, 147. 

 ', lichenoides Linn. f. Suppl. Plant. Sys 



) Steph. 

 pi. 74. 1776. 

 Veg. Ed. 13, 69. 



