382 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.57. 



For his larger divisions Foerster used many of the old Graven- 

 horstian characters supported by those of Holmgi-en, but added 

 many new ones to define his much finer subdivisions. He tabulated 

 and named many new genera, most of them without further diag- 

 nosis and without including any species or designating types. This, 

 together with the extremely minute differences which Foerster con- 

 sidered of generic value, makes the determination of his genera very 

 difficult. Indeed, many of them stand to-day without included 

 species. The difficulties in tliis respect are perhaps less in the 

 Ichneumoninae than in almost any other gi'oup, although even there 

 one must exercise considerable liberality in the interpretation of 

 characters to satisfactorily place a species in its genus. 



Practically all authors since Foerster have followed him very 

 closely . Especially is this true of Ashmead and Schmiedeknecht 

 whose keys are largely translations or adaptations of Foerster, with 

 new genera and new characters interpolated occasionally. 



Foerster's work, left unfinished as it was, has thi-own much light 

 on the classification of the Ichneumonoidea, but because of his un- 

 supported use of unisexual and variable characters it has also added 

 much to the confusion of this difficult group. 



Thompson. — In his treatment of the Ichneumoninae in his Opus- 

 cula En tomologica Thomson^ followed largely the System of Holmgren. 

 He published no tribal nor generic tables, but his keys to species 

 abound in new and useful characters. It is indeed unfortunate that 

 Thomson cUd not apply his clear insight to an attempt to clarify 

 the classification of the Ichneumonidae as a whole. No other 

 worker has appreciated as did he the extent of variation in the group 

 or the little dependence that can be placed in the superficial charac- 

 ters used for the separation of the larger groups. 



His contributions concerning the Icluieumoninae are scattered 

 through several fascicles of his Opuscula Entomologica and con- 

 sist largely of keys to Swedish species and observations on those 

 species. 



Davis. — In presenting his review of North America Tiyphoninae 

 Davis ^ gives, without gi'ouping them into subfamilies, a synopsis 

 of the tribes of the Ichneumonidae. This synopsis follows very 

 closely (so closely in fact that up to couplet 10 it is a translation) 

 Foerster's key of the natural families of Ichneumonidae, and has its 

 use mainly in being its author's interpretation of Foerster and in 

 giving a definition of the tribes he treats. 



>C. G.Thomson, Opuscula Entomologica, Lund, fascicles 5, 8, 9, 12, 13, 19, and 21,1873-1896. 

 * G. C. Davis, A Review of the Ichneumonid subfamily Tryphoninae, 1897, Trans. Amer, Ent. Soc, 

 vol. 24, pp. 193-348. 



