170 PLACODITJM. 



ference, but passing finally into scarcely effigurate forms ; yellow 

 or orange in 1, 2, 3, as are the apotkecia only in 4 and 5; the 

 other species being otherwise coloured. 



3. P. elegans (Link) DC.; thallus stellate-radious, appressed, 

 naked on both sides ; orange ; the linear, loose, branched divi- 

 sions convex and torulose, wavy, and more or less lacunose- 

 uneven, discrete or sub-iinbricate, or finally contortuplicate ; 

 apothecia smallish to middling-sized, zeorine or biatorine; of 

 nearly the same colour with the thallus, the thin margin mostly 



entire. Spores ovoid-ellipsoid, ^- mic. Parmelia^Fr. L. E. 



p. 114. Tuck. exs. n. 109. Nyl. Scand. p. 136. P. diversicolor, 

 Ach. Syn. p. 210, fide Nyl. 



On rocks, North America, Acharius Syn. 1814. Arctic Amer- 

 ica, from Newfoundland, De la Pylaie, and Great Bear Lake, 

 etc., Richardson, to Melville Island, E. Br., and islands of 

 Behring's Straits, Wright. Rocky Mountains, Hayden; Hall. 

 Organ Mountains, Texas, Wright. Eastern and Middle States, 



Halsey. The present species, in typical conditions, might 



easily be taken to differ from the next, as a foliaceous lichen 

 from a crustaceous ; and this is in fact exactly Schaerer's latest 

 judgment (Enum.). But we have, notwithstanding, strictly 

 crustaceous members of the group before us which certainly 

 appear to hang between P. elegans and P. murorum. A case of 

 this sort is presented by a western lichen (North Platte, accom- 

 panied by undoubted P. elegans, Hayden ; Montana, also so ac- 

 companied, M. A. Brown; Wyoming, Lapham; Nevada, Bo- 

 lander) marked by a crustaceous, dark-orange thallus, the whole 

 surface of which, instead of being pitted is roughened by minute 

 granules now like those of shagreen and now coarser, and which 

 becomes finally, in the Wyoming plant, as closely applied to 

 the substrate as any P. murorum, but yet appears on the whole 

 to descend rather from P. elegans. The lichen may be conve- 

 niently distinguished as the var. trachyphyllum. 



4. P. murorum (Hoffm.) DC. ; thallus crustaceous, orbicular, 

 closely adnate to the substrate, contiguous ; bright-yellow ; the 

 warted centre passing at the circumference into cut-crenate 

 lobules ; apothecia smallish, sessile, zeorine ; disk naked, orange- 

 red, the thicker thalline margin sub-crenate. Spores much as 



in the last, but perhaps, on the whole, larger. Parmelia, Fr. 



L. E.p. 115, a (excl. d-f.) Th. Fr. Scand. p. 170. 



