
be distinguishable from Biatora ; and Buellia,* similar* 
ly, from Zecidea. And the, whole Class may: be con- 
ceived, asin like manner passing into 1, a Colourless 
Series, especially characteristical of the higher tribes; 
_ and 2, a Coloured Serics, having its chief development 
in the lower ; series which, tabularized, so as to exhibit 
the sporal analogies, will be found perhaps significant 
as well of the relations of the genera, as of the. syste- 
matic value of the spores, . 
~ As seen from my own, necessarily much-limited point 
of view, the difficulties of this sketch of a method ap- 
pear to be overbalanced by its advantages, Gyalecta, 
as reconstructed, in at least the spirit of these observa- 
tions, by the younger Fries, offers one of these difficul 
ties; but no other instance has occurred to me, in true 
Lichens, of muriform spores in a genus belonging ap- 
parently to the Colourless Series. The group is a small 
one, and its relations to Thelotrema may be nearer than 
has been suspected. In the last-named large, mainly 
tropical, and protean natural genus, and in Graphis 
(less distinguishable from Opegrapha than Gyalecta from 
Thelotrema) there is certainly, at first sight, as great ap- 
parent confusion in the spore-features, as in the external 
conditions of the apothecia; but the species are here 
happily so numerous, that uncertainties of the latter 
sort are, in the widest view, perhaps readily explaina- 
ble ;—-and so, if I mistake not, with those of the former: 
both groups being typically referable, and as entireties, 
to the Coloured Series. There is moreover, to be ad- 
mitted generally, a possible distinction between colour- 
Bae EEE ee eee eee 
(*)Earlier than Rhizoearpon, Massal., which name can scarce- 
ly derive precedence from its use in a wholly distinct manner 
(as including namely types of three genera as understood by 
the Italian al er) by De Candolle, 
