A REVISION OF THE GENUS LOCUSTA, L. 



137 



It is, therefore, in full accordance with wliat Linnc meant by his genus Gryllus 

 Locusta, as well as with the formal laws of nomenclature, that migraioria, L., must be 

 regarded as the genotype of Locusta, L* 



Not less than 16 " species " have been described by different authors as belonging 

 to the genus Locusta, L. {=Pachytylus, Fieb.). This number, however, has been 

 reduced alreadv bv earlier revisers, who synonymised many species ; but W. F. 

 Kirby in his Catalogue (Syn. Cat. Orth., iii, 1910, pp. 221-231) still mentioned 

 seven distinct species. My investigations, however, have clearly demonstrated the 

 variability of the species of Locusta to an extent far greater than might have been 

 anticipated, and my conclusion, which will be fully proved presently, is that onlj" 

 two species can be distinguished, namely, migratoria, L., and panialina, Walk., 

 but the latter differs from migratoria in so many important characters that a new 

 genus is described below (p. 162) to include it, which I propose to call Locustana, g. n. 



III. Locusta migratoria, L., and its Forms. 



IVIorphological Characters and Variability of migratoria and danica. 



These two forms, if typical examples are studied, seem to be quite distinct from 

 each other in many morphological characters, and may be regarded, as has been done 

 by most authors, as two independent species. On the other hand, every extensive 

 collection includes specimens of Locusta that cannot be identified with certainty 

 with either migratoria or danica, but seem to represent intermediate forms. This 

 fact induced many authors to regard migratoria and danica as but extreme individual 

 aberrations of the same species. 



In studying this question I tried, first of all, to analyse carefully and impartiallyt 

 all the external morphological characters of both forms, as given by different authors, 

 studying them on as extensive a series of specimens as possible. 



After excluding all characters that at once proved to be too indefinite or simply 

 incidental, the following summary of differences between typical danica and migratoria 

 has been obtained : — 



L. migratoria (fig. 1, C, D, E.) 



Vertex convex, with a median longi- 

 tudinal keel ; fastigium separated from 

 frontal ridge by an angular transverse 

 keel. 



Pronotuni relatively shorter .Tnd 

 broader in metazona, with a distinct 

 construction before the middle ; fore 

 margin rounded ; hind angle rounded ; 

 median keel low, in profile straight or 

 even concave. 



Elytra^ relatively longer. 

 Hind femora relatively shorter. 



L. danica (tig. 1, A, B.) 



Vertex fiat, without median keel ; no 

 transverse keel separating fastigium 

 from frontal ridge. 



Pronotum relatively longer and more 

 compressed laterally, without or with 

 but feeble constriction before the middle; 

 fore margin angulatelj^ prominent ; hind 

 angle acute ; median keel high, tecti- 

 form, convex in profile. 



Elvtra relatively shorter. 



Hind femora relatively longer. 



* I am much indebted to Mr. J. H. Durrant for the help he has generously given me in the 

 solution of this question. 



t I must candidly confess that when starting my work I had only a very modest intention — 

 to find out characters for separating migratoria and danica, which I assumed beforehand to be 

 distinct specifically. The facts quickly destroyed my preconceived opinion and compelled me 

 to work deductively. 



t This important and rather striking difference between migratoria and danica was first noted 

 by the artist of the Zoological Museum in Petrograd, Miss O. M. Somina, who made drawings 

 of both insects for Mr. I. Shevvrev, and the latter drew mv attention to it. 



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