PTEROMALIDAE OF N.W. EUROPE 271 



Tridymus Ratzeburg, 1848 : 183. Type-species : T. aphidum Ratzeburg, by designation of 



Gahan Fagan, 1923 : 148. 

 Tripedias Forster, 1856 : 60. Type-species : Gastrancistrus [Tripedias) tripedias Boucek, 1964a, 



by subsequent reference. 

 Tridymus Ratzeburg ; Thomson, 1876a : 193-201. 

 Tridymus Ratzeburg ; Ashmead, 1904 : 273, 274. 

 Gastrancistrus Westwood ; Ashmead, 1904 : 273, 275. 

 Tridymus Ratzeburg ; Schmiedeknecht, 1909 : 274, 275, 276-277. 

 Gastrancistrus Westwood ; Schmiedeknecht, 1909 : 275, 276, 277-279. 

 Tridymus Ratzeburg ; Nikol'skaya, 1952 : 238. 

 Gastrancistrus Westwood ; Boucek, 1964a : 259-261. 

 Gastrancistrus Westwood ; Peck et al., 1964 : 34. 



The type-species of Glyphe Walker (autumnalis Walker) was transferred to 

 Gastrancistrus by Walker (1846 : 25). 



Tridymus Ratzeburg. Ratzeburg described this genus with three included 

 species : aphidum Ratzeburg, 1848 ; [Pteromalus'] salicis Nees, 1834 ! an d 

 xylophagorum Ratzeburg, 1848. Ashmead (1904) designated two different species 

 as type-species of the genus : Tridymus aphidum Ratzeburg on p. 273, Pteromalus 

 salicis Nees on p. 392. Gahan and Fagan (1923 : 148) adopted aphidum Ratzeburg 

 as type-species. This decision was unfortunate because aphidum has not been 

 recognized by any author subsequent to Ratzeburg. It might be more satisfactory 

 if Gahan and Fagan 's designation could be annulled and Pteromalus salicis Nees 

 adopted instead as type-species, which course would objectively define the genus 

 Tridymus. Dr. Boucek agrees with me on this point. An application may be made 

 to the International Commission on Zoological Commission on this change. 



Tripedias Forster. Described without included species. Boucek (1964a : 259) 

 described a new species Gastrancistrus tripedias (which he at the same time designated 

 as type-species of Tripedias Forster) from material in Forster's collection which with 

 little doubt represented that on which Forster had originally based his genus 

 Tripedias. 



The species of Gastrancistrus will certainly prove to be very numerous ; already 

 there is a large total for western Euope alone. One encounters some taxonomic 

 difficulties, particularly with regard to certain species-groups. For example there 

 are four closely allied species, not very easy to distinguish, in the group of fuscicornis 

 Walker. Especially troublesome situations exist in the species-groups of salicis 

 (Nees), vagans Westwood, and compressus Walker. In these groups, some of the 

 forms here treated as valid species differ only slightly inter se, and it is difficult in 

 certain cases to be sure whether some of them are really distinct or merely forms of 

 one variable species. Much further research is needed to clarify such problems, 

 and the present work should be regarded only as a beginning. 



Key to European Species 



(This key is intended primarily for the identification of females. In most cases it should also 

 help to refer males to their correct species-group.) 



1 Scutellum, except sometimes the axillulae, wholly reticulate, not noticeably 



more shiny than the mesoscutum ; in nearly all the species the scutello- 



