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SOME EECURRENT PHASES OF VARIATION IN 

 THE LARENTIIDiE. 



By Louis B. Prout, F.E.S.. 



I SUPPOSE no lepidopterist can take up the systematic study 

 of the variation in a particular family or genus, &c., without 

 being struck with the parallel lines upon which it runs in the 

 several species — a very evident suggestion, we may take it, of 

 community of descent. To be sure, many of the most frequently 

 recurrent phases of variation may almost as aptly be described 

 as characteristic of the whole order of Lepidoptera, subject only 

 to such limitations as are imposed by the nature of the general 

 colour-scheme or pattern ; and as some of these will be mentioned 

 in the following tentative notes, I might, if I had not held a 

 lengthy title inexpedient, have more accurately headed them 

 " Some Recurrent Phases of Variation in the Lepidoptera, as 

 especially exhibited in the LarentiidiE " ; but it is none the less 

 true that the emphasis, if one may so speak, of a particular type 

 of variation is often restricted to a comparatively few families or 

 genera, and that the student therefore gradually comes to asso- 

 ciate such type rather with these than with the Lepidoptera 

 eji masse. Take, for instance, the characteristic costal darkening 

 of Apamea opliiogramma, which appears again in one of the forms 

 of the allied A. seealis {didyma), but is absolutely unknown in 

 many other Noctuid genera, where it might conceivably have 

 occurred ; or, again, the pale costa which is apt to characterize 

 certain forms of many Agrotids — TripJicena promdja, Peridroma 

 saucia, Agrotis tritici, A. cursoria, &c. And even some other 

 variations, which appear in a wider range of unrelated genera 

 than these — such, for instance, as the suppression of certain 

 markings, or a variability in their position — are decidedly more 

 prevalent in some groups than in others. 



The distinctive types of marking of the Geometrides in general, 

 and of the Larentiidae in particular, seem to lend themselves to 

 the following frequent phases of variation, amongst others: — 

 melanism ; a narrowing of the central area, by approximation of 

 the first and second lines ; a breaking up of a normal " central 

 fascia " into lines, or, conversely, a consolidation of what are 

 normally mere lines into a " central fascia " ; and a suppression 

 of markings in the basal and marginal areas, often accompanied 

 by an intensification of them in the central. I want to call 

 attention here to some of the principal Larentid species ex- 

 hibiting these phases of variation, and I have called my notes 

 " tentative " because I have not yet given adequate systematic 

 attention to the matter, and am hoping, by writing on the 

 subject, to obtain supplementary information from fellow- 

 entomologists. 



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