l.Vl LICHENES. [Cetrtria. 



Mackay, as with the present species. The surface of the thallus is 

 usually downy. A pruinose or downy membrane expanded across the 

 involute surface of the apothecia at length bursts and displays the disk. 

 It is sometimes sprinkled with minute granular buds, when it resembles 

 too strongly P. aphthosa, 



4. P. polydactyla, ACH. Thallus naked, smooth, beneath re- 

 ticulated with brown veins; fertile lobules very numerous, 

 crowded, their sides, as well as those of the brown, terminal, 

 suberect; apothecia revolute. Ach. L. Un. p. 519. Dill. Muse. 

 t. 28. /. 107, 108. 



On moss, among grass and on banks ; frequent. This species is 

 very nearly allied to the preceding which sometimes has the apothecia 

 as numerous and crowded. 



29. NEPHROMA. Ach. 



Thallus foliaceous or coriaceous, lobed; apothecia borne on 

 proper lobules, orbiculate or reniform, the entire affixed to 

 the inferior surface of the thallus, by which, too, they are 

 bordered. 



1. N. resupinata, ACH. Thallus coriaceous thin, greyish- 

 brown when dry, dark-olive or lead-green when wet, the lobes 

 imbricated ; fertile lobules very short ; apothecia with the disk 

 of a red-brown. Ach. L. Un. p. 522. Eng. Bot. t. 305. 



On rocks and on old trees ; not uncommon. A pubescence of the 

 inferior surface of the thallus, noticed by authors is not always dis- 

 tinctly observable ; but, what is more remarkable, if that surface be 

 broken or abraded, a white cottony substance is found in the interior. 

 The buds appear as subrotund granules on the upper surface, oftener 

 affecting the edges, presently flattening, and expanding into new 

 fronds. 



30. CETRARIA. Ach. 



Thallus foliaceous or cartilagineo-membranaceous, lobate, laci- 

 niated, naked beneath. Apothecia orbiculate, obliquely ad- 

 nate to the margin of the thallus, partly unattached beneath ; 

 the disk coloured ; the border of the substance of the thallus. 



1 . C. glauca, ACH. Thallus membranaceous, somewhat shin- 

 ing, glaucous or brownish-grey, segments of the lobes lacero- 

 incised, ascending; buds granular, mostly marginal, grey or 

 brown ; apothecia elevated, the border rugose. Ach. L. Un. p. 

 509. Eng. Bot. t. 1066, andL.fallax, t. 2373. 



On rocks in the mountains ; not uncommon. The aged fhallus, in 

 some states, is reticulato-lacunose. The buds usually marginal, are 

 sometimes thinly scattered over the surface ; they may be observed ex- 

 panding into fronds. This plant varies much in colour of the upper 

 as well as the edges of the lower surface, and remarkably in the degree 

 of laciniation of those edges ; they are entire in specimens from Man- 

 gerton, while in those from Carig mountain, they are more incised and 

 finely cut than in the figure of English Botany. 



