four new British Lichens. 93 



the introduction of what I suppose to be a new species of this 

 tribe ; nor should I have ventured upon so doing, had I not be- 

 lieved the present plant to have been altogether overlooked by 

 authors. Yet, spite of this circumstance, it may be presumed, 

 from the various parts of the kingdom in which it has already been 

 found, that it is not of very uncommon occurrence. It generally 

 grows upon old trees, and not unfrequently in the hollow parts of 

 them, where it is immediately conspicuous by its numerous yel- 

 low shields. The indefatigable researches of Mr. Harriman have 

 also discovered it, though very sparingly, upon stone : but in this 

 case care must be taken to discriminate between it and L. aurel- 

 lus of Hoffman, from which it principally differs in the nature of 

 its crust, and in the shields assuming, as they grow old, the form 

 of tubercles. These two circumstances will also at all times keep 

 it separate from any of the appearances of L. candelarius, the crust 

 of which is always pale yellow and powdery. Instances may, 

 however, occasionally be found of the shields of that Lichen oc- 

 curring without any crust. But even in such case the two plants 

 are not to be confounded ; for the scutellae of L. candelarius are 

 almost always deeply concave, and are uniformly of a much 

 lighter colour, as well as larger size, than those of L. luteo-albus. 

 From L. cerinus, with which it agrees in crust, it differs in the 

 shields never having a white margin in their smaller size, and in 

 their being destitute of the greenish hue so remarkable in that 

 species. From Mr. Dickson's L. luteus, its leprous, inseparable 

 crust, its more pale shields, and the form they assume in an ad- 

 vanced state, equally separate it. The colour of the shields keeps 

 it likewise apart from L. rupestris of Acharius (L. calvus of Dick- 

 son), in which species they are considerably darker, and, when 

 young, are immersed in the very substance of the rock on which 

 they grow ; nor are they by any means either so numerous or so 



small. 



