250 Transactions. 



except where confirmed by other characters. When several genera of a 

 family have been established on normal considerations, and it is found that 

 a common variation tends to run through them, the employment of which 

 as a distinguishing character would split up the whole into pairs of closely 

 allied genera (the stalking or separation of veins 7 and 8 of the forewings 

 in the Glyphipterygidae is a case in point, though the same character is of 

 high importance in other families), it should not be so employed. 



The proposed alteration appears, then, from (1) to be undefinable, from 

 (2) to be unnatural, from (3) to be useless, and from (4) to be illogical. These 

 would seem to be all the possible lines of argument, and they all point to 

 the same conclusion, the rejection of the proposal. I find the. fourth sufficient 

 by itself ; but with the support of the other three (which could be extended 

 in detail if necessary) it ought to carry conviction. 



One other case in which Mr. Prout's views as to genera differ from mine 

 may be worthy of a short discussion. The two New Zealand and one 

 European species which I unite in the genus Epirrhanthis he treats as forming 

 three different genera. The purpose of genera is to unite species into groups 

 based on a natural community of origin, so as to provide an abridged notation 

 for their discussion as units in problems of phylogeny and geography. Mono- 

 typic genera are useless for this purpose (being simply species), and, though 

 sometimes necessary, should be avoided when possible. Now, Mr. Prout has 

 published his considered views on the Monocteniadae (to which Epirrthanthis 

 belongs) in the Genera Insectorum (under the title of " Oenochrominae "). He 

 admits these three genera to be nearly allied, for he places them together, 

 and produces nothing else as being nearly allied to them, the genera on each 

 side of them being remote ; the distinctions alleged between them are in 

 minor characters, which can be regarded as specific merely (it is often not 

 understood that not only all species, but all individuals, differ in structure) ; 

 it is true he treats one of the species (with doubt) as two, but there is small 

 justification for that course (he was perhaps misled by the difference in the 

 sexes) ; the aggregate of the three species can be defined as a whole (I so 

 define it in this paper) : what, then, is gained by keeping them separate ? 

 It can serve no object but a fancied equalization of generic standard, which 

 Mr. Prout has himself elsewhere admitted to be unrealizable : no two genera 

 are equivalent in value. Whereas by uniting them the interesting geo 

 graphical relation is clearly brought out and summarized under the single 

 head : we are substituting a genus which signifies something for three which 

 signify nothing. 



As to some other opinions expressed by my friend Mr. Prout in the former 

 paper quoted, it will be charitable to assume that they were not intended 

 fur publication. When, for example, he states that Selidosema " is a 

 European genus, and probably does not occur in New Zealand " (p. 53), 

 the argument seems defective, in view of the fact that all the largest New 

 Zealand genera of Lepidoptera without exception are European. I add as 

 a further generalization that they are always common European genera, 

 and that they are never equally well developed in Australia. A more correct 

 inference would have been that as the group of New Zealand species in ques- 

 tion is a considerable one, therefore it is most probably European. 



Again, when Mr. Prout recommends distinguishing euclidiata from cata- 

 pyrrha by the absence of red on the underside, " until it can be proved that 

 they are conspecific," he seems to be wholly unaware that euclidiata is an 

 Australian species, with double areole, and ciliated antennae of male, whilst 

 catapijrrha has single areole and pectinated antennae (fully explained by 



