36 1. VERRUCARIACEAE [7. Thrombium 



yses soon becoming gelatinized; asci broadly clavate; spores 1-8, hyaline to 

 brown, oblong to ellipsoid, transversely and longitudinally septate. 

 The algal host is Protococcus. 



A. Spores commonly more than 30 fx in length 



B. Perithecia minute to small, 0.1-0.3 mm. across 1. S. clopima 



B. Perithecia small to middle-sized, more than 0.3 mm. across 



C. Thallus zonate at the margin 4. S. circinata 



C. Thallus not zonate at the margin 2. S. umbrina 



A. Spores 15-22 X 9-12 fi 3. S. diffractella 



1. Staurothele clopima (Wahl.) T. Fries, Nov. Act. Soc. Sci. Ups. III. 3:363. 



1861. 

 Verrucaria clopima Wahl.; Ach. Vet. Akad. Nya Handl. 152. 1809. S. umbrina 



var. clopima (Wahl.) Tuck. 

 Thallus thick, rough, warty or becoming areolate, widespread or broken up 

 into smaller irregular areas, brown to dull black; perithecia minute to small, 

 0.1-0.3 mm. across, immersed in the thallus, except the depressed ostiole; spores 



2, brown, oblong, 7-13-septate transversely and 3-5-septate longitudinally, 30-48 X 

 12-20 fx. (Plate 1 b.) 



On rocks, New Hampshire and Minnesota. 



2. Staurothele umbrina (Ach.) Tuck., Gen. Lich. 258. 1872. 

 Lichen umbrinus Ach., Lich. Suec. 14. 1798. S.lithina (Ach.) Zahlbr. 

 Thallus rather thin, smooth, becoming granulose or areolate, widespread or 



often broken up into smaller irregular areas, olive-gray to dusky-brown; perithecia 

 small to middle-sized, 0.3-0.6 mm. across, immersed in raised areas, the black 

 apex finally protruding; spores 2, brown, oblong, 7-11-septate transversely and 

 3-5-septate longitudinally, 30-48 X 12-20 fi. 



On rocks, from New England to Florida and westward to the Rocky Mountains. 



3. Staurothele diffractella (Nyl.) Tuck., Gen. Lich. 258. 1872. 



Verrucaria diffractella Nyl., Mem. Soc. Acad. Maine et Loire 4:33. 1858. 

 Plialostauris diffractella (Nyl.) Clements. S. petersii Tuck, nomen nudum. 



Thallus moderately thick, chinky-areolate, widespread or broken up into 

 smaller irregular areas, ashy or yellowish to olive-brown; perithecia minute to 

 small, 0.1-0.3 mm. across, immersed in raised areas, or more or less of the black 

 apex finally protruding; spores 8, hyaline, ellipsoid, 5-7-septate transversely and 

 1-2-septate longitudinally, 15-22 X 9-12 fx. 



On rocks, from New England to the Gulf of Mexico and westward to Missouri 

 and Minnesota. 



4. Staurothele circinata Tuck., Gen. Lich. 257. 1872. 



Thallus round to somewhat irregular, zonate at the circumference, becoming 

 chinky, hypothallus darkening, fimbriate, olive-brown; perithecia middle-sized, 

 0.4-0.7 mm. across, located toward the center of the thallus, immersed in subhemi- 

 spherical raised areas, or the upper portion finally protruding, black; spores 1-2, 

 brown, oblong to ellipsoid, often narrower toward one end, 9-15-septate trans- 

 versely and 3-5-septate longitudinally, 34-50 X 16-20 /x. 



On calcareous rocks, Trenton Falls, New York. 



7. Thrombium Wallr.. Fl. Crypt. Germ. 3:287. 1831. 



Thallus crustose, smooth or minutely granulose, partly or wholly within the 

 substratum, devoid of differentiation into layers; apothecia minute to small, more 

 or less immersed, the wall complete, the ostiole minute; hypothecium hyaline to 

 brown; hymenium hyaline; paraphyses delicate, commonly persistent; asci clavate 

 or cylindrical; spores 8, hyaline, ellipsoid or oblong-ellipsoid, non-septate. 



The algal host is Protococcus. 



