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The genus is distinguished from ParmeHa by a purely technical character. 

 In the spermagonia of ParmeHa, 

 the spermatia are borne laterally 

 from joints of the sterigmata 

 ("fulkren endobasidial" of Zahl- 

 bruckner, see text-figure 2) while 

 in Parmeliopsis the spermatia 

 are terminal only ("fulkren exo- 

 basidial," see text-figure i). This 

 distinction would be of doubtful 

 generic value if it were not for 

 the fact that these species ob- 

 viously form a natural group, Sterigmata and spermatia of Parmeliopsis (fig. i) and 

 not conveniently classified with P^rmelia (fig. 2). Semi-diagrammatic, 

 either Parmelia or Cetraria. It is an advantage, therefore, to have a name to 

 designate the group, and Zahlbruckner (Engler and Prantl: Die Natiirlichen 

 Pflanzenfamilien, Teil I, Abteilung I,* p. 209, 1905) has accepted Nylander's 

 name and conception of the group. 



The generic name to be used is, however, of less importance than the question 

 of the specific names. But before discussing the nomenclature it will be well 

 to have in mind the distinctive characters of the plants that are to be considered. 

 There are four species, all foliose, and more or less closely appressed to the fence- 

 rails, or to the bark of conifers upon which they grow: 



A. A lichen with gray upper side, whitish under side, radiating lobes, and en- 



tirely free from isidia or soredia (Plate XX, fig. i). 



B. A lichen with gray upper side, whitish under side, occurring in two forms: 



the typical form with radiate lobes and dense isidia (Plate XX, fig. 2), and 

 a variety with irregular lobes and scattered isidia (Plate XX, fig. 3). 



C. A lichen with gray, often dirty-looking, upper side, and dark (castaneous 



to black) under side, with radiate lobes and powdery white soredia (Plate 

 XX, fig. 5). 



D. A lichen with straw-colored or sulphury upper side, dark (castaneous to 



black) under side, more or less radiate lobes, and soredia which are sulphury 

 to distinctly yellow (Plate XX, fig. 4). 



To give some idea of the confusion that exists, it may be pointed out that 

 the name placorodia has been applied to forms A and B, the name aleurites to 

 forms B and C, the name diffusa to forms B, C, and D. The isidiose plant, B, 

 has been called placorodia, aleurites, diffusa, and ohsessa! 



The writer has adopted the names u.sed in this paper after a careful study 

 of all the types in the herbarium of Acharius. After repeated attempts to obtain 

 information in regard to Weber's type of diffusa from the curator of the her- 

 barium at Goettingen, without receiving any reply, it has been necessary to 

 depend upon Weber's original description. This is, however, a long and detailed 

 description, and as will be shown can apply to one of these plants only. 



