76 PHYSCIA. 



1823. New England, not uncommon. Canada, Macoun. Cali- 

 fornia, Bolander. Oregon, Hall British Columbia, Macoun. 

 The lichen is obviously the analogue, in the stellaris- group, of 

 P. comosa in the speciosa- group ; and the appressed forms of the 

 former cluster stand in a similar relation to those of the latter. 

 P. stellariSj as here taken, belongs especially to the colder 

 regions of the earth. On this continent we find it beginning to 

 be modified even in New England ; and this process of differen- 

 tiation continues as we go southward. Neither of the three New 

 Granada lichens of Lindig's Collection (n. 712, 731, 2602) referred 

 by Nylander to his P. stellaris is (in the published specimens) a 

 satisfactory representative of the northern plant. We may then 

 perhaps expect this, as it approaches, or enters inter-tropical 

 regions, to assume new forms, abhorrent no doubt from the 

 merely northern conception of the species, and requiring to be 

 determined from a wider point of view. But if this diminish as 

 well the systematic value of the generally accepted P. astroidea, 

 P. crispa, P. dilatata, etc. (as assumed in the writer's earlier 

 review of the American Physcice, cited above), it may be said to 

 enhance, from a comparison of the equally accepted P. comosa, 

 the value of the now generally undervalued P. hispida. 



8. P. ccesia (Hoffm.) Nyl. ; thallus crustaceous-cartilagine- 

 ous, stellate, pale ash-coloured, besprinked with rounded, grey 

 soredia ; beneath pale, now ash-coloured, and blackening, with 

 black fibrils; lobes pinnately many-cleft; apothecia smallish, 

 sessile, the soon naked and black disk bordered by a thin, in- 

 flexed, sub-entire margin. Spores bilocular, ^ mic. Nyl. 



Syn. 1, p. 426. Parmelia, Fr. L. E. p. 83. Tuck. Lich. exs. 

 n. 86. 



Old stone walls. Pennsylvania, Mulilenberg Catal. 18.18. 



New York, Halsey ; Sartwett. Massachusetts, Tuckerman. 



Our plant (Lich. Amer. n. 86) is in all respects like the Euro- 

 pean ; but I have seen but little of it. 



9 P. obscura (Ehrh.) Nyl. ; thallus sub-membranaceous, or- 

 bicular and appressed (unless in inuscicoline states) epruinose, 

 glaucous-cinerascent becoming livid or brown, now sorediifer- 

 ous ; beneath black, and more or less densely black-fibrillose ; 

 lobes dichotomously many-cleft, flattish, sub-ciliate, now pass- 

 ing at the centre into minute, imbricated lobules; apothecia 

 smallish to scarcely middling-sized, sessile, the exciple more or 



