PLACODIUM. 169 



XXX. PLACODIUM (DC.), Naeg. & Hepp. 



Apothecia sub-scutellaeform j either regular (lecanorine), 

 or shewing also a proper margin (zeorine), or only the lat- 

 ter (biatorine), the disk, for the most part, yellowish-orange. 

 Spores ellipsoid, polar-bilocular (rarely of the more common 

 bilocular type, or, more rarely yet, simple), colourless. Sper- 

 matia oblong, or staff-shaped ; the sterigmas almost always 

 multi-articulate. Thallus crustaceous j either lobed at the 

 circumference ; or, very rarely, suffruticulose ; or uniform 5 

 oftener more or less yellow. 



* Tli amnoma. Thallus Jruticulose ; orange. 



1. P. coralloides, Tuckerm. j thallus slender, solid, cartila- 

 gineous, decumbent j bright -orange -yellow; branches terete, 

 nodulose, obtuse, sub-dichotomously divided ; apothecia of mid- 

 dling size, lateral and terminal, somewhat elevated, zeorine ; the 

 flattish, rough, dark-orange disk bordered at length only by the 

 thin, entire, proper margin, which is finally excluded. Spores 

 oblong, the sporoblasts approximate, the isthmus deficient, ^ 

 mic. Obs. Lick. 3, I c. p. 287. 



Maritime rocks, near San Francisco, California (Bolander), 

 Tuckerman I. c. 1864. The biatorine apothecia bordered more 

 or less, or coronate, with the finally powdery nodules of the thal- 

 lus ; l-2 mm - wide. 



2. P. cladodes, Tuckerm. ; thallus short, slender, solid, erect, 

 made up of terete, fastigiately branched, pale trunks, which 

 blacken below, and are crowded together into a caespitose, papil- 

 late, orange-yellow crust ; apothecia small, sessile ; the flat, pow- 

 dery, fulvous disk sub-marginate, bordered by a stout, crenulate, 

 thalline margin. Spores solitary, obtuse-ellipsoid, the spore- 

 cells connected by an isthmus, ^^ mic. Obs. Lich. 3, I. c. 



p. 265. 



On the earth, in the alpine regions of the Kocky Mountains 

 (Hall), Tuckerman L c. 1864. Looking like an uniform, warted 

 crust. Apothecia about l mra - wide. The short thekes have not 

 been seen to contain more than a single spore, which is at first 

 brownish. 



* * Euplacodium. Thallus typically lobed at the circum- 



