2 Studies in the Hybrid Bistoninae. 1 V 



Non-Boarmioid Subgroup; (2) the Boarmioid Subgroup. At present 

 we are only concerned with that small homogeneous portion of the 

 former which includes the genera Lycia, Poecilopsis and Nyssia. Of 

 these three, Lycia is fully winged in both sexes, whilst the other two 

 are endowed with apterous females. From these circumstances alone 

 it appears certain that Lycia is the oldest genus, although its primitive 

 character may be confirmed in many independent ways. For instance, 

 so closely is Lycia allied to Megahiston plumosaria, one of the generalised 

 species at the head of the two subgroups, that if a female of that 

 species were captured in England it would be regarded as a very minor 

 aberration of X. hirtaria. Further, applying the well-known test of 

 great discontinuity in geographical distribution to determine the age 

 of a genus, we find that Lycia displays that phenomenon to a marked 

 degree, its species existing in widely separated colonies in Europe, 

 North Africa, Eastern Asia and Eastern North America — a range 

 neither equalled in extent nor in discontinuity by either of the other 

 genera Poecilopsis or Nyssia. ' 



The genus Poecilopsis consists of four species, three being restricted 

 to Europe and one to North America, whilst Nyssia, likewise com- 

 prising four species, is exclusively European. In outward appearance 

 there seems to be little to suggest which of the two is nearer to the 

 Lycia stem, but fortunately there are in reality several very important 

 structural characters available as evidence, and nothing is more weighty 

 than that supplied by the genitalia. Considering the male armature of 

 all eight species we find that they fall into two groups, one with rounded 

 valves comprising Poecilopsis pomonaria and P. isabellae, and the other 

 with pointed valves including the remaining half dozen species. 



Making due allowance for size, those of the former pair are indis- 

 tinguishable from those of L. hirtaria whilst those of P. lapponaria and 

 P. rachelae approach those of Nyssia zonaria in much the same way. 

 This feature in itself forges a chain linking up two species of the genus 

 Poecilopsis with Lycia and two with Nyssia, thereby assuring us that 

 Poecilopsis has been derived from Lycia, and Nyssia from Poecilopsis. 



On the other hand all four Poecilopsis species, in common with 

 Lycia, have the male vesica armed with strong cornute, those on the 

 same organ in Nyssia being obsolete or obsolescent ; similarly in the 

 female genitalia Poecilopsis agrees with Lycia in the possession of an 

 arrowhead-shaped signum on the bursa copulatrix, and this signum 

 Nyssia lacks entirely. These two observations combined emphasise the 

 essential unity of the genera Poecilopsis and Nyssia within themselves. 



