172 PLACODIUM. 



fulvous j rimose-areolate, passing at the circumference into short, 

 paler, white-powdery, crenate lobes; apothecia small, zeorine; 

 the flat, rufous disk bordered by a thin, crenulate, thalline mar- 

 gin. Spores ovoid-ellipsoid, ^-mic. Suppl. 1,1 c. p. 425. 



On limestone, Texas ( Wright), Tuckerman 1. c. 1858. Best 



comparable perhaps externally, except in colour, with the Euro- 

 pean Lecanora circinata. Apothecia O mm -, 5 to O mm -, 8 in width. 



7. P. galactophyllum, Tuckerm. ; thallus crustaceous-adnate, 

 areolate-squamulose ; white and mealy ( becoming yellowish- 

 brown when rubbed), the areoles passing at the circumference 

 into crenate lobules ; apothecia small, zeorine, adnate, flat ; an 

 obtuse, entire thalline margin bordering the dark-orange, mar- 

 ginate disk. Spores ^ mio. Obs. lAch. 4, 1. c. p. 171. 



Lime-rocks, Chase county, Kansas (Hall), Tuckerman Gen. 



1872. Apothecia of the size of those of n. 6. When this and 



the last are more fully known, they may possibly prove to be 

 nearer akin than appears. 



8. P. peliophyllum, Tuckerm. ; thallus crustaceous, adnate, 

 verrucose ; cinereous-glaucous (and blackening) with a laciniate, 

 linear-multifid circumference ; apothecia of more than middling 

 size, sessile ; the disk chestnut-brown, the stout, entire thalline 



margin finally flexuous. Spores ellipsoid, ^ mic. Gen. Lich. 



p. 108. 



On granitic rocks, Yosemite Valley, California (Bolander), 

 Tuckerman I. c. 1872. The specimens of this marked lichen 

 were only obtained with difficulty, and are scanty. It should be 

 further studied where it grows. Apothecia exceeding 2 mm - in 

 width. 



9. P. variabile (Pers.) Nyl. ; thallus crustaceous, adnate, 

 rimose-areolate ; lurid-ash-coloured ; the areoles of the circum- 

 ference scarcely now effigurate; apothecia of middling size or 

 smallish, adnate, rather flat; the dark-chestnut (blackening) 

 disk bordered conspicuously by a white (powdery) entire at 

 length flexuous margin, which is now concolorous with the disk ; 

 or obsolete, and the apothecia lecideoid. Spores ellipsoid, ^ 

 mic. <Nyl. Scand. p. 138. 



b. atro-album, Tuckerm. ; thallus yellowish-brown ; apothe- 

 cia small, distinctly zeorine ; a thin, demiss, white thalline mar- 



