Knight. — On the Lichenographia of New Zealand. 347 



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 Pertusarice importance is always attached to the extra- 

 ordinary thickness of the sporal envelope, which often consists of three or 

 more laminas ; and this characteristic, when the paraphyses are implexo- 

 ramose, is of the highest importance. Indeed, the presence of implexo- 

 ramose paraphyses has induced Professor Midler to transfer several 

 Lecanora} to Pertusaria. In a paper on the lichens of New South Wales 

 (Linn. Trans. Botany, second series, vol. 2) I called attention to Professor 

 Muller's remarks (Flora, 1879, No. 39, 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 Pertusarice, 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 Bay, — " Methodum intelligo 

 nature convenientem qua? nee alienas species conjungit, nee 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 it 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 generic 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 Lecidece into several genera and group the new genera in 



