10 Journal New York Entomological Society. [Voi. xviii. 



characters of two recurrent nervures and a complete cubital vein. 

 Such a type is represented by the genus Lysiognatha Ashmead ('95) 

 but this form has the peculiar exodont mandibles of the Alysiidse 

 which on this account cannot be considered a part of the stem from 

 which the Braconidae and Ichneumonidae have been derived, although 

 I believe they represent an offshoot not far from it. In the Miocene 

 at Florissant Alysiidae occur apparently in about the same proportion 

 as they do in recent times. There is one other remarkable type 

 with exodont mandibles, Vanhornia, recently described by Crawford 

 ('09), but its affinities are so problematic that it can hardly enter into 

 the present discussion. So far the family Agriotypidae has not been 

 found fossil, and any conclusions regarding its relationships must 

 be derived from taxonomic studies alone. 



Several families of the Proctotrypoidea have been discovered fossil, 

 the Proctotrypoidse, Belytidse, Diapriidae, Ceraphronidae and Scelioni- 

 dae, but with one exception all the genera are apparently identical with 

 recent ones and none give any clue to the probable origin of the 

 group. 



The same is true of the Cynipoidea, with the exception of one 

 genus Protoibalia (Brues, '10) from the Miocene shales of Floris- 

 sant which shows characters transitional from the genuine Cyni- 

 pids to the Ibaliinae. 



Although the paleontological evidence concerning the origin of 

 the foregoing families is scant it leads to a few general conclusions 

 and they agree well with those derived from anatomical studies of 

 the same families. 



There is another family, the Bethylidae, well represented in amber 

 by some genera, which, taken in connection with a number of recent 

 ones, indicate very nicely part of the line of evolution within this 

 group. 



It is a generally accepted fact that the older and more stable 

 groups of animals, particularly those which are decadent from a 

 paleontological standpoint, are the least adaptive, while those at pres- 

 ent on the ascendent are better fitted to survive and prosper under 

 changed conditions of environment. 



The importance of this principle to the economic entomologist is 

 at once apparent in connection with all attempts to introduce and 

 naturalize parasitic insects with a view toward checking the increase 



