86 14. ARTHONIACEAE [47. Arthonia 



30. Arthonia byssacea (Weig.) Almq., Kgl. Svensk. Vet. Akad. Handl. 17:25. 



1880. 

 Sphaeria byssacea Weig., Obser. Bot. 42. pi. 2, f. 9. 1772. A. bijormis (Floerke) 



Schaer. A. bijormis f. develata (Nyl.) Willey. 

 Superficial thallus thin, whitish, smooth, becoming powdery; apothecia minute 

 to small, 0.2-0.3 mm. across, adnate, round to irregular, often elongating, reaching 

 0.5-0.7 mm. long, the disk flat to convex, dark brown to blackish, sometimes prui- 

 nose; tinged faintly red within; hypothecium darker; asci ovoid-ventricose ; spores 

 oblong-ovoid, 3-5-septate, one end cell larger, 12-24 X 6-9/*. 

 On trees, Massachusetts and New Hampshire. 



31. Arthonia glaucescens Nyl., Mem. Soc. Nat. Cherb. 5:337. 1857. 

 Superficial thallus dull grayish white to greenish gray, often bearing small, white, 



mealy soredia, sometimes disappearing; apothecia middle-sized, 0.75-1.25 mm. 

 across, immersed, round to somewhat irregular, the disk flat, obscurely whitish 

 pruinose to brown or blackish; hyaline or tinged pale yellow within; spores hya- 

 line, ovoid-ellipsoid, 3-septate, 18-30 X 5.5-8.5 fx. 

 On trees, Massachusetts and North Carolina. 



32. Arthonia cinereopruinosa Schaer., Enum. Lich. Eur. 243. 1850. 

 Superficial thallus thin, ashy white, smooth to slightly rough, becoming pow- 

 dery; apothecia minute to small, 0.09-0.3 mm. across, partly immersed to adnate, 

 round to slightly irregular, the disk flat to convex, dusky to black; hyaline within; 

 asci pyriform; spores hyaline, ovoid-ellipsoid, 3- or rarely 1-4-septate, one end 

 cell larger, 15-18 X 4-6^. 



On trees, White Mountains, New Hampshire. 



33. Arthonia Tuckermaniana Willey, Syn. Arth. 20. 21. 1890. 



Thallus thin, smooth, white to ashy; apothecia numerous, minute, 0.1-0.2 mm. 

 across, the disk flat to slightly convex, reddish brown to black, sometimes pruinose ; 

 hyaline to brownish within; spores oblong-ovoid, 3-5-septate, the cell at one end 

 larger, hyaline to brown, 16-23 X 5-6 /x. 



On trees, Florida. 



34. Arthonia Eckfeldtii Mull. Arg., Bull. Herb. Boiss. 3:48. 1895. 



Thallus thin, continuous, smooth to sometimes slightly powdery, white and 

 shining or grayish, sometimes bordered by a thin, obscure line; apothecia small, 

 0.3-0.6 mm. across, closely adnate, round to irregular, the disk flat to convex, 

 reddish brown to brownish black; brownish within; asci broadly ellipsoid; spores 

 8, hyaline, oblong-ellipsoid, 3-septate, 13-16 X 4.5-6 fi. 



On trees, Florida and Louisiana. 



35. Arthonia leucastraea Tuck., Gen. Lich. 220. 1872. 



Superficial thallus thin to moderately thick, dull white, smooth, becoming pow- 

 dery; apothecia minute to small, 0.15-0.2 X 0.4-0.6 mm., partly immersed, oblong 

 to elongated, the disk flat, reddish brown, more or less pruinose ; hypothecium dark 

 brown; hymenium tinged pale yellowish; spores oblong-ovoid, hyaline, 3-septate, 

 end cells larger, middle cells sometimes divided longitudinally, 12-16 X 5.5-7.5 ft. 



On trees, Texas. Transitional between Arthonia and Arthothelium. 



36. Arthonia glebosa Tuck., Gen. Lich. 221. 1872. 



Superficial thallus thick and rough, composed of round, elevated, dusky squam- 

 ules; apothecia small, 0.3-0.5 mm. across, partly immersed to adnate, often clus- 

 tered, round, the disk convex, black; tinged pale brownish within, hypothecium 

 darker; asci pyriform; spores hyaline, oblong-ovoid, 1 -septate, constricted, one cell 

 slightly larger, 11-16 X 4.5-6 fi. 



On rocks and soil among mosses, Colorado, California, and Washington. 



