PLACODIUM. 173 



gin bordering a black and naked, marginate disk. Spores obso- 

 letely polar-bilocular (the spore-cells mostly approximate), ^|? 



mic. Obs. Lich. 4, I c. p. 172. 



a, Jurassic rocks, Rocky Mountains (Hay den), Tuckerman 

 Gen. 1872. Ancient potsherds, Utah, Dr. Palmer (Herb. Wil- 



ley). b, cretaceous sandstone, and chalcedony, North Platte, 



Rocky Mountains, Hayden. Lime-rocks, Utah, Lapham. P. 



variabile is associable, through P. chalybceum (not as yet de- 

 tected here), with the effigurate species of the genus, but loses 

 at length every trace of a lobed margin. This is quite deficient 

 in b, which was referred by me at first to the near neighbourhood 

 of Lecanora erysibe. Another state of P. variabile with de- 

 pauperate or obsolete thallus and wholly black (lecideoid) apo- 

 thecia (on limestone, Alabama, Peters) is best comparable with 

 the European form Agardhianum, at least as exhibited in a speci- 

 men from herb. Koerb. ; upon which compare this author's ob- 

 servation in Parerg. p. 68. 



* * * Callopisma. Thallus not effigurate (though now 

 squamulose) uniform ; the fruit more or less orange, except in 

 n. 20, 21, 22. 



f Spores polar-bilocular, except in 18; in eights. 



10. P. bolacinum, Tuckerm. ; thallus squamulose ; tawny- 

 yellow; the scattered scales coarse, convex, glebous-difform, 

 finally crenate ; apothecia middling-sized, sessile, soon convex ; 

 the orange, rusty-powdery disk with a thin, concolorous margin, 



the thalline one mostly obsolete. Spores ellipsoid, ^ mic. 



Lich. Calif, p. 18. 



On sandstone and serpentine rocks (and what is perhaps the 

 same on mud walls), on the coast of California (Bolander), Tuck- 

 erman I. c. 1866. Apothecia l mm - to more than 2 mra - wide. 



11. P. cinnabarrinum (Ach.) Anz.; thallus rimose-areolate 

 and sub-effigurate ; or the now scattered areoles passing from the 

 first into often applanate and crenate-lobulate scales; them- 

 selves crowded together at length into a sub-imbricate crust ; 

 becoming dark-orange ; apothecia minute, adnate ; disk orange, 

 the paler margin entire. Spores ellipsoid, -^ mic. Leca- 

 nora, Ach. L. U. p. 402. Parmelia, Fr. L. E. p. 165. 



A common rock-lichen throughout the United States, inhab- 

 iting alike granitic and calcareous rocks, from New England to 





