144 GUIDE TO THE STUDY OF LICHENS. 



large, lateral or terminal. Disk reddish-brown. Spores 

 colorless, typical, 16/w, X 7.5/i. 



7. Theloschistes leucomela. Thallus fruticose, much 

 branched, lobes uniform, flat, long, ciliate ; gray above, 

 lighter beneath. Apothecia large, margin ciliate. 

 Disk dark-gray. Spores light-brown, large, 51/x X 



This is a southern species and a very handsome 

 plant. Fine specimens from Lower California have 

 come to my notice. It would have been perhaps more 

 correct to classify this lichen with Physcia, in accord- 

 ance with Lindsay and others. 



VI. PARMELIACEyE.^ 



In this family the thallus varies from typically 

 crustose to typically foliose and fruticose. In all 

 forms above the crustose types the thallus is much 

 branched. The apothecia belong to the thalline type ; 

 they are discoid, and attain their maximum size in 

 such genera as Usnea, Parmelia and Peltigera. 



The position and limitation of the family are depend- 

 ent upon the following characters: 1. The absence 

 of stipes and podetia excludes it from the Caliciacece 

 and CladoniacecE. 2. The presence of the thalline 

 apothecia excludes it from the Lecidiacece. 3. The non- 

 union of the spore-cells excludes it from the Physciacece. 

 4. Presence of discoid sessile apothecia separates it 

 from the Graphidacece and Verrucariaceoe. 5. The 



1 In the study of most of the genera of this family I received speci- 

 mens from the collection of my friend W. W. Calkins, for the use of 

 which I express my sincere gratitude. 



