Kxienr.—0On the Lichenographia of New Zealand. 847 
Arthonia described in the present paper, with the exception of A. aspera 
(n. sp.), in which the lamina sporigera is more or less carbonized and 
degraded. 
In respect of the Pertusarie importance is always attached to the extra- 
ordinary thickness of the sporal envelope, which often consists of three or 
more laminz ; and this characteristic, when the paraphyses are implexo- 
ramose, is of the highest importance. Indeed, the presence of implexo- 
ramose paraphyses has induced Professor Müller to transfer several 
Lecanore to Pertusaria. In a paper on the lichens of New South Wales 
(Linn. Trans. Botany, second series, vol. 2) I called attention to Professor 
Müller's remarks (Flora, 1879, No. 89, p. 484) in which he advocates these 
transfers, and I noticed that, in my opinion, besides L. parella and L. 
pallescens, there are other species liable to similar removal; for instance, 
L. verrucosa, and L. calcarea. Hepp, together with Nylander and Th. Fries, 
has placed Lecanora bryontha, Ach., with the Pertusarie, an arrangement 
amply supported by the great thickness of the parietes of the solitary spores 
and the implexo-ramose paraphyses. It may be added that the presence of 
intricate ramose paraphyses with thick double sporal envelopes renders it 
necessary that Lecanora gemmifera, Th. Fries, should also be transferred to 
Pertusaria. P. fumosa (n. sp.) of the present paper has a thin sporal 
envelope. 
I have read with some interest in the Flora (1882, p. 458) Dr. Nylander's 
objections to break up a large genus of closely-allied species and dispose of 
them in several genera. We all agree with Ray,—‘‘ Methodum intelligo 
nature convenientem que nec alienas species conjungit, nec cognitas 
separat." But it seems to be contended by Dr. Nylander that cognate 
species, however numerous they may be, ought not to be separated into 
genera and that no limiting number of species can be assigned to a genus. 
Certainly there is no reason why we should fix upon an arbitrary limiting 
number, which i& would be improper to exceed; although, on the other 
hand, it may be desirable that genera should not be overburdened with 
species. One of the objects of classification is, that the generic name, 
like an algebraic formula, should be the symbol of certain characteristics 
of all the species included in the genus and these are stored in our 
memory. 
To take an instance. There are not much less than 500 species at pre- 
sent arranged under Lecidea, a genus which is limited by a small number of 
characters. Is it not a real disadvantage to the progress of a science that 
the generie name in this instance conveys to the mind so little of the nature 
and organization of any one of the 500 species. On the other hand, if we 
break up the Lecidee into several genera and group the new genera in 
