— 75 — 



thin, 12-15/1 in thickness, with minute lumina, about 2/x in diameter. Apothecia 

 rare, 1-3 mm. in diameter; disk badious or darker, flat becoming convex; thalline 

 margin subentire, or crenulate, becoming thin. Spores oblong, straight or curved, 

 IQ-12X2-3M. Spermagonia minute, immersed in the thallus, and indicated by 

 a darkened spot on the surface. 



Specimens examined from: Alaska, Northwest Territory, British Columbia, 

 Alberta, Greenland, Newfoundland, Maine, New Hampshire, Vermont, 

 Massachusetts, New Jersey, Virginia, South Carolina, Alabama, Michi- 

 gan, Wyoming, Colorado. 



Exsiccati: Decades N. A. Lich. no. 108. Macoun Canad. Lich. no. 239 in part. 

 The color will distinguish this from any other species of the present genus. 



Sorediate species of Cetraria with similar coloration have the soredia confined 



to the margins. The only species of Parmelia that has comparable characters 



grows on rocks. 



4. Parmeliopsis diffusa (Weber) Riddle comb. nov. 

 Lichen Weber Spicil. Flor. Goett. 250. 1778. 



Parmeliopsis aleurites Nyl. according to specimens in Mus. d'Hist. Nat. 



Paris! Not Parmelia aleurites Ach. 

 Parmelia hyperopia Ach. Syn. Lich. 208. 18 14. Th. Fries Lich. Scand. 



120, 1871, according to type-specimen! 

 Parmeliopsis hyperopia Arnold Flora 62: 329. 1879. Wainio Medd. 

 Soc. F. et Fl. Fenn. 6: 127. 1883. Zahlbr. in Engler & Prantl: Natur- 

 liche Pflanzenfamilien, Teil I, Abteilung L* p. 209. 1905. 

 Parmelia ambigua var. albescens (Wahl.) Schaer. Enum. Lich. Europ. 47. 

 1850. Tuck. Syn. N. A. L. 1: 66. 1882. 

 Thallus suborbicular, 1.5-3 cm. in diameter, closely adherent to the sub- 

 stratum, whitish to cinereous or subfuscescent above, smooth and even nitid 

 toward the circumference, rimulose and becoming broken at the center, with 

 more or less elevated balls of soredia, which are typically white, sometimes dirty- 

 cinereous, scattered or densely packed towa,rd the center, rarely becoming an 

 efifused, powdery mass (this condition less common than in P. ambigua) never 

 isidiose. Remaining characters as in P. ambigua. 



Specimens examined from: Alberta, Ontario, Labrador, Maine, New Hamp- 

 shire, Washington. 



Exsiccati: Decades N. A. L. no. 109. Macoun Canad. Lich. no. 239 in part. 



In spite of the undeniably close relationship of this species with the pre- 

 ceding, it would seem logical to consider it a valid species rather than a variety, 

 since the difference between ochroleucous and cinereous coloration is recognized 

 to be of constant specific value in both Cetraria and Parmelia. The whitish 

 soredia will distinguish Parmeliopsis diffusa from any other species of the genus, 

 and also from any American species of Cetraria. It is much smaller than most 

 species of Parmelia. It might possibly be confused with depauperate and ad- 

 herent specimens of Parmelia physodes, which grows on the same substrata and 

 is often sorediate, but in that species the soredia are always confined to the tips 

 of the lobes. From sterile specimens of such sorediate Physcias as Ph. crispa 



