SCIENTIFIC NOTES. 109 



of the wing in length, and in another more than one-third, is sufficient, 

 if found constant and clearly perceptible ; but in practice it would 

 probably be a very bad character, ^ as probably some species would be 

 transitional. Even where transitional forms are not known, it will 

 always be nei:essary to use judgment as to whether the distinction 

 employed is of such a character as to be likely to hold good in the 

 event of the discovery of additional species. But even where there is 

 a good and definite point of distinction, it does not follow that the 

 genera are to be maintained ;- where genera are small and numerous, 

 it becomes mtrmsically undesirable to multiply them, and in such a 

 case, if two small genera agree in nearly all structural characters, 

 resemble one another superficially, are apparently closely connected 

 genealogically, and finally are capable of accurate definition and dis- 

 tinction as a single whole, then they ought in general to be united. 

 Many structural characters are variable, either in different specimens of 

 the same species, or sometimes in a transitional series of closely allied 

 species. I hope shortly to give a paper on the classification of the 

 European Geometrina, and shall then give some remarkable, and, I 

 believe, unprecedented statistics of the variation of structural characters, 

 liut many instances will be found in the following genera. The same 

 point of structure will often be found available as a good and reliable 

 distinguishing character in one instance, and not in another ; this can 

 never be determined except by actual consideration of the particular 

 circumstances. Nor can it be said beforehand what characters are 

 likely to be good ; perhaps the most suspicious are tufts of hairs, 

 especially when developed as secondary sexual characters, when they 

 are often 'unreliable'" {Trans. Ent. Soc. Lond., 1890, p. 430). Mr. 

 Meyrick's ideas may be sound, and if the genera which he has united, 

 did agree in nearly all structural characters, did resemble one another 

 superficially, were apparently closely connected genealogicallv, and 

 finally, were capable of accurate definition and distinction as a whole, 

 there would perhaps not be much harm done ; but do roboraria and 

 wavaria, duhitata and blandiafa, dolobraria and fasciaria, or stcbnotata 

 and vi'.albata fulfil these conditions ? If so, how ? Is a genus with a 

 dozen "ors"in it " accurately defined and distinguished"? Having 

 now considered this paragraph, we may consider how it works out. 

 Mr. Meyrick makes a genus with fixed characters ; he finds a moth or 

 two fits into it. He finds another species which agrees pretty well 

 with everything but the palpi, and he adds " or " to his characters and 

 admits this species ; he finds another agreeing pretty g:>nerally, but 

 failing in another character, another "or " is added, and s .) on ; e.g., of 

 Diastictis, Hb., he writes : — "Face with appressed scales or short ridge 

 or tuft of projecting scales. Palpi moderate, porrected or subascending, 

 rough scaled. Thorax soi/ieiinies crested posteriorly, fiiore or less hairy 

 beneath. Femora glabrous or rarely slightly hairy ; posterior tibiee in 

 (J ojten dilated, with all spurs present. Fore-wings in ^ with fovea, 



^ Nothing shows the absolute lengths to which those who are simply students of 

 the characters of the imago may have to resort for a character, if, as Mr. Meyrick 

 practically admits, such a case as this is possible. 



- It would be interesting to know what is to determine this, and how Mr. Meyrick 

 has settled it. From Mr. Meyrick's statement it would appear that a character, 

 which would be accepted to break up a large genus, might be ignored, even if of 

 equal value, to unite two small ones. 



