48. Arthothelium ] 15. GRAPHIDACEAE 95 



On trees, from New England to Florida, and westward to Illinois, reappear- 

 ing in California. 



10. Arthothelium albovirescens (Nyl.) Fink n. comb. 



Arthonia albovirescens Nyl.. Bull. Torr. Club 16:105. 1889. Allart hot helium 

 albovirescens (Nyl.) Zahlbr. 



Superficial thallus thin, greenish white, obscurely scurfy; apothecia minute, 

 0.06-0.1 mm. across, partly immersed to adnate, round and often clustered, the 

 disk convex, brownish black to black; hyaline within; asci ovoid-pyriform; spores 

 hyaline, oblong-ellipsoid, 8-13-septate transversely and 2-3-septate longitudinally, 

 15-35 X 10-16 ft. 



On trees, Florida, and doubtfully reported from Alabama and Louisiana. 



The smaller, scarcely muriform spores of the original description were immature. 

 In material examined, spores were partly the same. 



11. Arthothelium macrothecum (Fee) Mass., Ric. Lich. 55. 1852. 

 Arthonia macrotheca Fee, Essai Crypt. Suppl. 42. 1837. 



Superficial thallus thin, smooth to rough, yellowish ashy to whitish, becoming 

 powdery and disappearing; apothecia middle-sized to large, 0.6-3 mm. across, 

 round to irregular, usually subsuperficial, the disk white-pruinose to brownish black 

 or black; asci ovoid-pyriform; spores hyaline, ellipsoid, 9-17-septate transversely 

 and 3-7-septate longitudinally, 46-68 X 17-28 it. 



On trees, Texas. 



12. Arthothelium interveniens (Nyl.) Zahlbr., Cat. Lich. Univ. 2:127. 1922. 

 Arthonia interveniens Nyl., Act. Soc. Sci. Fenn. 7:482, 483. 1863. 

 Superficial thallus thin, smooth to slightly rough, greenish gray to ashy; 



apothecia small to middle-sized, 0.4-0.8 mm. across, partly immersed to adnate. 

 oblong to slightly irregular, scattered or 2 or 3 in a group, the disk flat, brownish 

 black to black; dark-colored within; spores hyaline to brown, oblong-ellipsoid, 

 4-7-septate transversely and 1-2-septate longitudinally, 21-30 X 8-10 it. 

 On trees, Florida, Louisiana, and Texas. 



13. Arthothelium Hallii (Tuck.) Zahlbr., Cat. Lich. Univ. 2:126. 1924. 

 Arthonia Hallii Tuck., in Willey, Syn. Arth. Suppl. 55. 1890. 



Superficial thallus thin, smooth, ashy white, bordered wholly or in part by 

 a black line; apothecia minute to small, 0.15-0.5 mm. across, wholly or partly 

 immersed, round to more often irregular, often clustered, the disk flat, brownish 

 black to black; hyaline within; asci ovoid-pyriform; spores hyaline, oblong-ovoid 

 to oblong-fusiform, 5-6-septate transversely and 1 -septate longitudinally, 20-32 X 

 7-10 it. 



On trees, Illinois. 



OTHER SPECIES REPORTED 



Arthothelium adveniens Nyl. — California. 



Arthothelium violascens var. subcinerascens (Nyl.) Zahlbr. — Ohio. 



15. GRAPHIDACEAE 



Thallus crustose, partly within the substratum, showing little or no differentia- 

 tion, attached to the substratum by hyphal rhizoids; apothecia usually elongated, 

 often curved, more or less branched, rarely round, single or clustered but not in a 

 stroma, the proper exciple usually well developed, sometimes covered by a thin, 

 thalloid layer; paraphyses unbranched or branched and interwoven, usually per- 

 sistent. 



The algal hosts are Palmella and Trentepohlia. 



A. Spores hyaline or rarely brownish 



B. Spores non-septate 49. Xylographa 



