UCHENES. 31 



Gc. Apothecia adnati to the surface of the thallus 

 near th> margin, often on special erect lobes. 



Peltigera. Apothecia borne on the upper surface of the 

 thallus. 



Nephroma. Apothecia borne on the lower surface of the 

 thallus. 



4 c. ThaUus crustaceous, mostly uniform, sometimes 

 lobulate, rarely crustaa ous-Jruticulose. 



Placodium. Differs from Theloschistes only through its 

 erostaoeouB thallus. 



Lecanora. Differs from Parmelia only through its crusta- 

 oeoos thallus. 



Pertusaria. Apothecium usually consisting of several hy- 

 menia (easily to be mistaken for angiocarpous ones), all imbedded 

 in a much swollen thalline exciple common to them all. Spores 

 usually less than eight in an ascus, mostly of comparatively 

 large size. 



8 b. Thallus gelatinous when icet. 



Collema. Thallus foliaceous or sometimes ascendant and 

 fruticulose, mostly dark green, the cortical layer usually indis- 

 tinct ; gonidia in chains dispersed through the thallus. 



Leptogium. Thallus mostly lead-colored, cortical layer dis- 

 tinctly parenchymatous, otherwise as in Collema. 



'2 b. Apothecia. circular or nearly so, margined only by a 

 proper exciple; hymenium soon becoming convex 

 or cephaloid, and growing over the exciple. 



9 a. Thallus foliaceous. 



Umbilicaria. Thallus attached to the substrate at a single 

 point. Apothecia g}TOse-plicate. 



9 b. ThaUus consisting of a vertical portion (podetia) 

 which may be cylindrical and branched or simple, 

 club-shaped or funnel-formed ; and a horizontal 

 portion ichich may be foliaceous, squamulose or 

 granulose, often appearing as lateral outgrovt],* 

 from the podetia. Sometimes the thallus consists 

 only of iu deed, hollow podetia. 



