15. Arthopyrenia ] 4. PYRENULACEAE 45 



B. Apothecia oblong, reaching 1 X 0.8 mm 4. M. oblongata 



A. On rocks 3. M.aterrima 



1. Microthelia micula Koerb., Syst. Lich. 373. 1855. 

 Pyrenula cinerella (Nyl.) Branth. et Rostr. 



Thallus rudimentary or absent or imbedded in the substratum and indicated 

 by a whitish area; perithecia minute to small, 0.1-0.4 mm. across, dimidiate, semi- 

 or more deeply immersed, round, or becoming oblong on birch, the superficial 

 portion strongly convex, often depressed, black; spores 1 -septate, oblong-ellipsoid, 

 10-18 X 5-9/*. 



On trees, from New England to Florida and westward to Missouri and Minne- 

 sota. 



var. quadriloculata (Fink) Zahlbr., Cat. Lich. Univ. 1:263. 1922. 

 Pyrenula cinerella var. quadriloculata Fink, Cont. U. S. Nat. Herb. 14:239. 1910. 

 Spores becoming 2-3-septate, perhaps smaller than above. 

 On trees, Minnesota and Florida. 



2. Microthelia thelena (Ach.) Trevis., Cons. Verr. 10. 1860. 



Verrucaria thelena Ach., Syn. Lich. 92. 1814. Pyrenula thelena (Ach.) Trevis. 



Thallus very thin, ashy to greenish gray, disappearing, or imbedded in the 

 substratum and indicated by a whitish or yellowish area and surrounded by a 

 black line; perithecia minute to small, 0.1-0.4 mm. across, dimidiate, the superficial 

 portion convex, dilated below, black; spores 1-septate, constricted at the septum, 

 oblong-ellipsoid, 16-30 X 7-10 /i. 



On trees, Florida. 



3. Microthelia aterrima (Anzi) Zahlbr., Cat. Lich. Univ. 1:255. 1921. 

 Rinodina aterrima Anzi, Comm. Soc. Critt. Ital. 2:11. 1864. M. MetzleriLahm. 

 Superficial thallus widespread, thin, granulose or scurfy, greenish black to dull 



black; perithecia minute to small, 0.1-0.4 mm. across, superficial portion convex, 

 the ostiole depressed, becoming much dilated, black; spores 1- rarely 3-septate, 

 slipper-shaped, 14-19 X 5-8 /i. 



On rocks, Nevada and California. 



4. Microthelia oblongata Mull. Arg., Flora 68:332, 333. 1885. 



Pyrenula oblongata Willey. 



Superficial thallus very thin, smooth, widespread, white to yellowish; perithecia 

 middle-sized to large, oblong, 0.6-0.8 X 0.9-1.1 mm. or narrower and trident- 

 shaped, the superficial portion concave to flat, dilated below, black; spores becoming 

 1-septate, oblong-ellipsoid, 14-18X7-8 /*. 



On trees, Massachusetts. 



5. Microthelia Willeyana Mull. Arg., Flora 68:332. 1885. 

 Pyrenula Willeyana (Mull. Arg.) Willey. 



Thallus thin, ashy to brownish, intersected and bordered by black lines, some- 

 times disappearing; perithecia minute to small, 0.2-0.4 mm. across, dimidiate, the 

 superficial portion black, hemispherical, dilated below; spores brownish to brown, 

 1-septate, one cell larger, oblong-ellipsoid, 22-24 X 8-9 /i. 



On trees, Massachusetts and Illinois. 



15. Arthopyrenia Mass., Ric. Lich. 165. f. 326-41. 1852. 



Thallus crustose, more or less within the substratum, the superficial portion 

 thin, smooth, irregularly widespread, whitish or ashy; perithecia minute to small 

 or middle-sized, more or less immersed, the superficial portion black, subconical 

 to hemispherical, the ostiole minute and often inconspicuous, the wall dimidiate 

 or rarely complete; paraphyses branched and interwoven, becoming somewhat gelat- 

 inized; spores 8, hyaline, ellipsoid-oblong to linear-oblong, 1-3-septate, unseriate, 



