PAKtfARIA. 127 



21. P. Petersii, Tuckerm. ; thallus squamulose-foliaceous, 

 membranaceous, stellate-expanded ; from livid-glaucous becom- 

 ing olivaceous, and black; lobes appressed, flat, contiguous, 

 now dispersed and soon falling away at the centre ; radiant and 

 many-cleft at the concentrically disposed circumference ; the 

 hypothallus obsolete; apothecia very small, biatorine, flat, 

 black, with a thin margin. Spores ellipsoid and oblong, simple 



and bilocular, decelerate, ^^ mic. Gen. Lick. p. 54. Lecidea, 



Tuck. Pterygium, Nyl. Syn. p. 93. 



Calcareous rocks. Alabama (Peters] Tuckerman in Nyl. 

 Syn. 1858. New York, Wittey. The regular, stellate, con- 

 centrically disposed thallus is not always to be seen ; but only 

 scattered lobules. 



22. P.flabellosa, Tuckerm.; thallus squamulose-foliaceous, 

 membranaceous ; livid- ash -coloured; lobules narrow-linear, 

 dissected, those of the circumference expanded and fan-shaped, 

 flat, and longitudinally striate ; those of the centre teretish and 

 heaped; upon an indistinct, finally blue-black hypothallus; 

 apothecia very small, immixt, flat ; a red disk bordered by a 

 pale -livid margin, and both finally blackening. Spores oblong- 

 ellipsoid, 2-4-locular, decelerate, ^^ mic. Obs. Lich. I. c. 5, 



p. 401 ; Gen. Lich. p. 54. 



Granitic rocks. Vermont (Frost), Tuckerman I. c. 1862. 



White Mountains, Willey. Apothecia 3-6 mic. wide, about 



twice the size of those of the last. 



23. P. nigra (Huds.) Nyl. ; thallus very minutely squamu- 

 lose ; leaden-ash-coloured; squamules now scattered and lobu- 

 late, but heaped, for the most part, into a broken, granulose or 

 corallinoid crust; upon a thin, blue-black hypothallus; apo- 

 thecia very small, biatorine, sessile (from reddish-brown) com- 

 monly black, the swelling disk soon excluding the thin margin. 



Spores oblong, 2-4-locular, decolorate, ^^ mic. Collema, 



Ach. L. U. p. 628. Pannaria, Nyl. Scand. p. 126. 



b. ccesia, Nyl. ; thallus dark-gray, or whitish ; the internal 



structure confused and obscure. Tuckerm. Gen. Lich. p. 54. 



Collolechia, Mass., Koerb. Syst. p. 377. 



Calcareous rocks, and sandstones, Pennsylvania and the 

 northern States to Canada, Muhlenberg Catal. 1818. Illinois 

 and Kansas, Hall Alabama, Peters. b, calcareous rocks, 



