OETHOPTERA. 295 



specimens with broad scales, some were much lil<c the leaves of 

 Salisbnria atliaiitijnlia in shape and appearance. 



One cannot help speculating on how such racial differences can 

 occur, especially since the curious circumstance appears that Bacot's and 

 Whittle's specimens, from localities not very far apart (Hertfordshire 

 and Essex) are very definitely different, whilst those from south 

 Switzerland are intermediate. 



The explanation appears to be tluit in a parthenogenetic species 

 like this the ordinary effect of frequent crossing in maintaining a 

 uniform aspect of a'species in continuous areas has no place. In L. 

 lapidella, or any ordinary species, a variation occurring in Switzerland 

 might perchance establish itself, without being affected by type forms 

 existing in England, say Hertfordshire ; but if it occurred in Essex, 

 crossing with the Hertfordshire form, directly even, or at anyrate 

 through the individuals occuring in the intermediate area, would 

 inevitably result in its being swamped, or, under rare conditions, in 

 its swamping the type ; in any case we should find the forms in Hert- 

 fordshire and Essex fairly identical (I omit reference to such cases as 

 Mr. Tutt shows us probably occur in AutJnvcrra). 



In a parthenogenetic species however, there would be no such cross- 

 ing ; in one locality even, say Essex, a variety occurring would not be 

 swamped by crossing, and it would be purely a question of natural 

 selection, whether the variety or type survived. If the variety was the 

 victor in the struggle then we should have a form in Essex different 

 from that in Hertfordshire, and in a wingless form Yikeft'irhaultdla, it 

 would take a long time for the improved Essex form to invade and 

 eject the type from Hertfordshire. Nor could it succeed in doing this 

 if the type form was, in fact, better adapted to Hertfordshire conditions 

 than the new variety. 



Parthenogenesis in fact forms a very effective segregating agency 

 for the formation of new species. The difference between lapuldla ? 

 lunl ferc/iaidtdla was probably very rapidly established on the latter 

 becoming parthenogenetic, and the several forms of the latter may or 

 may not be regarded as distinct species very much according to eacli 

 one's taste or prejudices. Interfertility is certainly not a test 

 applicable to settle any doubt on the (Question. 



(g) RTHOPTERA. 



Notes on the Decticidae with descriptions of new species. 



By MALCOLM BUllll, F.Z.S., F.E.S. 



The Ih'ctiridar are one of the most interesting families of the 

 Locustodea. Strange to say, they have not yet received adequate 

 treatment at the hands of orthopterists and have not yet been mono- 

 graphed. There are nearly 150 species known to science, distributed 

 througli 86 genera. At one time they were considered characteristic 

 of the palcearctic region, where certainly they attain their greatest 

 development, but in recent years a considerable number has been 

 taken in the nearctic region. They seem to prefer a temperate 

 climate, for, outside the " holarctic " region, only a few scattered 

 genera, poor in species, are known from South Africa and Australia. 

 They are large and active insects, with powerful jaws, and chiefly 



