33 



where the cortical layer is wanting. Gonimous stratum of both 

 kinds. A small genus occurring throughout. 9 spp. 



Genus 18. Eeioderma. Apoth. scutellaef orm , marginal on the 

 now extended lobes. Spores simple, at length colorless. Thallus 

 villous and now veiny beneath, with a pannose hypothallus ; the cor- 

 tical layer there wanting. Gonimous stratum of gonimia. A small 

 tropical genus, of which 1 sp. occurs in Mexico. 



Genus 19. Solorina. Apoth. innate on the upper side of the 

 thallus, the margin obsolete. Spores 2 loc, brown. Th. frondose, 

 villous beneath. Gonimous stratum of both kinds. A small genus 

 of temperate regions. 2 spp. 



Fam. 5. Pannaeiei. Thallus horizontal, frondose-foliaceous, 

 or, most commonly, squamulose ; mostly more or less lead-colored ; 

 imposed upon a conspicuous but now obsolete hypothallus. Go- 

 nimous stratum almost universally of gonimia. 



Genus 20. Endocaepisctjm. Apoth. mostly indicated only by 

 an ostiole, but finally emergent and scutellseform. Spores minute, 

 colorless, very numerous in the thekes. Thallus foliaceous, peltate, 

 the hypothallus deficient. Gonimous stratum of gonimia. A small 

 genus, of which we have 2 spp. 



Genus 21. Heppia. Apoth. orbicular, immarginate, more or 

 less sunken in the minute, frondose-squamulose thallus. Hypo- 

 thallus obsolete. Spores simple, colorless. Gonimous stratum of 

 gonimia. A small genus, of which we have 3 spp., one of them 

 undescribed. 



Genus 22. Phtsma. Apoth. scutellseform. Spores simple, col- 

 orless. Th. foliaceous, with a nap-like hypothallus. Gonimous 

 layer of gonimia much like those of Collema. A small genus, of 

 which we have 3 spp., two of them tropical. 



Genus 23. Pannaeia. Apoth. now scutellseform and Lecano- 

 rine, now zeorine, and now biatorine. Spore's simple, or 2-4 loc, 

 or rarely muriform, fuscesceut or decolorate. Th. monophyllous, 

 or multifid, or most often squamulose, becoming subcrustaceous. 

 A large and difficult genus, throughout. 24 spp. 



Fam. 6. Collemei. Thallus frondose-foliaceous, more or less 

 gelatinous when wet ; becoming squamulose or crustaceous ; lead- 

 colored or blackish-green ; the hypothallus almost always obsolete. 

 Gonimous layer of gonimia. 



Subfam. 1. Lichinei. Thallus frutieulose, the gonimia consti- 



