396 PROCEEDINGS OF THE AMERICAN ACADEMY 



of P. astroidea, and in others which pass imperceptibly into P. stel- 

 laris. These conclusions are results of much, oft-repeated study of 

 large collections of specimens, in numerous states of development and 

 degeneration. The smooth, normal Lichen, as it occurs in Texas and 

 Cuba, may be referred, with equal right, to P. astroidea or P. stellaris. 

 And the more northern, sorediate form (P. ohsessa, Acli.) only differs 

 from sorediate European' states in the greater size and regularity both 

 of the thallus and the soredia. But in tropical America, our plant 

 departs much farther from its type, acquiring not merely a greater 

 smoothness and elegance, but becoming entirely black beneath (P. ob- 

 sessa, Montag. Cuba, 1. c), a condition which now resembles, in general 

 habit, the present variety ; is now larger, on rocks, with the aspect of 

 P. stellaris ; and finally, occurs on trees, with all the characters, except 

 the color of the under side, of P. Pomingensis, Montag. Acharius de- 

 scribes his P. ohsessa as black beneath, while I have always found the 

 northern form, here referred to his species, pale on the under side ; but 

 there is no reliance to be placed upon this character in the specimens 

 from Cuba and Nicaragua, which occur, entirely similar above, but 

 now black and now pale-fuscous beneath, and varying in the same 

 manner in the color of the little ring of fibres which often surrounds 

 the base of the thalline exciple. 



Var. y. DoMiNGENSis : stellata, nuda, platyphylla ; laciniis planis 

 margine ssepius pulverulentis subtus pallidis. Parmelia {Physcia) Do- 

 mingensis, Montag. Cuba, p. 225 ; Nyl. Enum. Gen. 1. c. p. 106. On 

 trees. Seaboard of South Carolina, Mr. Pavenel. Key "West, Florida, 

 Dr. Blodgett. Louisiana, Dr. Hale. Bottoms of the Blanco, Texas, 

 Mr. Wright. Passes into the last variety, in Cuba ; and an entirely 

 smooth state, from the Bonin Islands, near Japan (U. S. N. Pacif. 

 Expl. Exp. Mr. Wright), exhibits at once the larger and wider lobes 

 of the present, and the smaller and more divided ones of var. astroidea. 

 But the American Lichen is almost always and elegantly characterized 

 by its powdery margins. The plant also approaches P. speciosa, var. 

 gramdifera (P. gramdifera, Ach. Syn.), especially that state with pow- 

 dery margins (P. granulifera, Meissn. in Hb. Kunz.), but is always, so 

 far as my specimens go, distinguishable from that, by a certain diver- 

 gence of habit, resulting in part from a different lobation ; the wider 

 and always flat divisions of P. Domingensis, Montag., with their reg- 

 ular palmate summits and slightly notched lobules, contrasting with 



