134 HERRE 



Of the eleven genera recognized by Zahlbruckner, we have two, 

 which are by far the most important members of the family. 



KEY TO GENERA. 



Thallus without distinct cortical layer, beneath naked. XXXII. Collema 

 Thallus with distinct cortex on upper side or both sides; under surface 

 naked or more or less covered with fleecy rhizoids. 



XXXIII. Leptogium 



XXXII. Collema (Hill.) A. Zahlbr. 



Collema Killer, Hist. PL 1751. 



Collema A. Zahlbr. Ascolichenes, 171. 1907. 



Thallus foliaceousor sometimes sub-crustose, very small to medium 

 size, very dark green or blackening; the under surface naked, 

 usually wrinkled or fenestrate; cortical layer not present or very 

 indistinct. Apothecia scattered or crowded, usually numerous, 

 circular, usually dish- or shield-shaped, very small to medium size, 

 lecanorine, a proper margin lacking or present; spores ellipsoid or 

 needle or spindle-shaped, bilocular, plurilocular, or muriform. 



A large genus, of wide distribution, the species growing upon bark, 

 mosses, earth, and rocks. 



KEY TO THE SPECIES. 



A. Confined to trees. 

 B. Surface with anastomosing edges covered with black granules. 



i. aggregation 

 BB. Surface radiately wrinkled and pustulate. 



C. Surface smooth, naked 2. vespertilio 



CC. Surface isidiose-pulverulent 3. nigrescens 



A A. Confined to earth and rocks. 



D. Thallus minute squamulose or crustose 4. cristatellum 



DD. Thallus not squamulose or crustaceous. 



E. Spores bilocular 5. coccophorum 



EE. Spores 4-locular to muriform. 

 F. Thallus rather large, smooth, pustulate and wrinkled ; apoth- 



ecia small 6. pulposum 



FF. Thallus usually only a border to the large, crowded, im- 

 beded apothecia 7. glaucescens 



i. COLLEMA AGGREGATUM Nyl. 



Collema aggregatum Nyl. Mem. Soc. Sci. Nat. Cherb. 2 : 318. 1854. 

 Collema aggregatum Tuck. Syn. N. Am. Lich. I: 146. 1882. 

 Collema aggregatum Herre, Proc. Wash. Acad. Sci. 7: 376. 1906. 



