04 Mi'- Tu R n' E u's Descriptions of 



sltiali. Il is now many years since I first found L. luteo-albus on 

 elfiis at Acle in Norfolk ; Mr; Dickson showed it to me growing 

 plentifully on lime trees at Croydon, and I have lately found it 

 on willows at Coltishall. 



4. Lichen porric.inosus. 



L. crusla tenui pulverulenki albo-virescente : scutellis fuscis; ju- 



nioribus niveo-marginatis concavis, adultioribus tuberculifor- 



mibus. 



Tab. VIII. Fig. 4. 



Innascitur ulmi montanae cortici apud Caistor prope Yarmouth. 



Crustam habet tenuem, pulverulentam, sparsam, e granulis minu- 

 tissimis, globosis, neutiquam cohaerentibus, constantem ; sic- 

 cam albam, madidam pallide virescentem, Byssumque botry- 

 oidem valdfe simulantem. Scutellae huic insident rarae, subro- 

 tundne, magnitudine fere Ervi seminis, initio concavae, disco 

 fuscse, margine niveau ; progrediente a?tate fiunt plana?, mox 

 convexae et tuberculiformes, marginis omnino expertes. Made- 

 factae ceraccam quandam et fere subdiaphanam praestant spe- 

 ciem ; siccatae atro-fuscae evadunt. 



The situation which naturally belongs to this Lichen, at least 

 among the British species, is between subfusevs and vemalis, with 

 both Avhich it has points of striking affinity. Its shields in colour 

 approach nearly to those of the former, but differ in regularly 

 assuming, as they grow old, the shape of tubercles ; and, still 

 more strongly, in their border, while young, being of a snowy 

 white, and of a substance quite dissimilar to the crust; whereas 

 the scutellae of L. subfitscits are for the most part more concave in 

 age than in youth, and their margin always appears not only to 

 be homogeneous with the crust, but also in general to be a mere 



elevation 



