92 THE ENTOMOLOGIST. 



THE GENUS PCEGILOPSIS (Harkison). 



By J. W. H. Harrison, B.Sc. 



Part L — Preliminary Pvemarks. 

 As I have pointed out elsewhere, the " genus " Biston, as 

 represented in Staudinger's ' Catalogue,' is a very heterogeneous 

 collection, comprising elements from no fewer than six distinct 

 genera. These are : — 



Biston (Leach); type stratarius. 



Lycia (Hiib.); type hirtaria. 



Ithysia (Kuh.); type zo7iaria. 



Poscilopsis (Harrison) ; type pomonaria. 



Apocheima (H. S.) ; type hispidaria. 



Microhiston (Stgr.) ; type lanarius (Ev.) (= tartaricus (Stgr.) ). 

 It was originally my intention to take these genera in turn, 

 and to deal with each of the species in all its stages in detail. 

 The imagines of the genus Ithysia have already been discussed, 

 and the treatment of the other forms postponed in order to give 

 time for the completion of the life-histories of Ithysia grcecaria, 

 I. alpina, and I. italica, but it has been found impossible to rear 

 (even in a hothouse) these exclusively Southern forms. In the 

 meantime, however, I am glad to say that I have been able to 

 secure, and describe at length, the early stages of all of the species 

 in the genus Poecilopsis, and therefore propose to complete my 

 work in that section now. This genus was described in Lepid. 

 Comp. fasc. vii. p. 344, and I have but little to add to the 

 description given there, except that one very important observa- 

 tion has been made which justifies further my separation of 

 these species from Ithysia. This is the fact that, whilst the 

 chromosome number in Ithysia is 112, in Poecilopsis it is 56, and 

 in Lycia 28. 



It has become imperative that I should take up this genus 

 now, because I have discovered in the course of my studies that 

 the Central European form that passes for P. lapp>onaria is not 

 that insect at all, although, fortunately, our Scotch insect is so. 

 Not only is this true, but, in addition, the two forms fall into two 

 different sections of the genus, which contains four species form- 

 ing two closely allied groups of two. These groups are : — 

 The two species Poecilopsis lapponaria and P. rachelce. 

 The two species P. pomonaria and P. isabellce. 

 The first group is probably Northern in its origin, for P. lap- 

 ponaria ranges from Lapland to Livonia, and then reappears in 

 Scotland ; whilst P. rachela is widely distributed in America, 

 from Montana and Manitoba along the Mackenzie Valley to 

 Alaska. The other group is of Central European origin, pomo- 

 naria having its headquarters in North Central Germany, but 

 extending, although sparsely, to Eastern France, Scandinavia, 



