. A guide to the study of lichens. ish to gray. Apothecia convex, brown to black. Spores seven to nine-celled, indistiiactly septate, colorless, 31/a X 2/x. 6. Bacidia rubella. Thallus of distinct, more orless scattered granules, greenish to gray. Apotheciaof medium size. Disk reddish-brown to colorless, nine to eleven-septate, 50/x X 4/x. 7. Bacidia suffusca. Thallus thinly granular, green-ish to ash-gray. Apothecia of medium size to quitelarge, raised margin. Disk reddish-brown coated witha translucent whitish film, giving it a characteristicappearance. Spores se
. A guide to the study of lichens. ish to gray. Apothecia convex, brown to black. Spores seven to nine-celled, indistiiactly septate, colorless, 31/a X 2/x. 6. Bacidia rubella. Thallus of distinct, more orless scattered granules, greenish to gray. Apotheciaof medium size. Disk reddish-brown to colorless, nine to eleven-septate, 50/x X 4/x. 7. Bacidia suffusca. Thallus thinly granular, green-ish to ash-gray. Apothecia of medium size to quitelarge, raised margin. Disk reddish-brown coated witha translucent whitish film, giving it a characteristicappearance. Spores seven to nine-celled, colorless,50/x X V 8. Bacidia Schweinitzii. Thallus granular, form-ing a thin crust, greenish to ash-gray. Apothe-cia of medium size. Disk brown to black. Sporescolorless, seven to nine-celled, 55/x X 4/x. 6. Lecidea. The representatives of this genus resemble theBiatoras very closely, so much so in fact that itwould seem advisable to combine the genera. Theonly essential difference seems to be the greater pre-. 28 J ILATi: I^. (rust,,SI- Typfs. Kimi, il.,- ,-,-t ion ut (l;irk 111 tli« lifibaliiiiii «•! iln- ( aliloinia »-iii> <iScience. Ltrhlta inh-i-nlfurti. GENERA AND SPECIE^. Ill dominance of dark coloration in the Lecideas, espe-cially in the disk and hypothecium. The Lecideas arealso more brittle. As in Biatora, the spores are sim-ple, elliptical and colorless. The majority of the species occur upon rock, someupon trees and fences. They play a very importantpart in the disintegration of rock. The Lecideas have the widest range of distribution:they occur at all latitudes and altitudes. Lecidcageographica occurs far above the line of perpetualsnow ; it forms the last vegetation of the Andes, theHimalayas and the arid peaks of Nova Zembla. 1. Lecidea panceola. Thallus consists of ratherthick, closely crowded squamules, which are convexabove and of irregular outline ; ash-gray to dirtybrown. Apothecia comparatively large ; sometim
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