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. IJarriman have 
also discovered it, though very sparingly, upon stone: but in this 
case care must be taken to discriminate between it and L. atirel- 
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 to 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. 
