2 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 



there liave been two well-marked lines in the phylogcny of the 

 suborder, the Tenthrediuid and the Sirieid steins. The Xyelidte 

 and Pamphiliidiv are very primitive forms that represent off- 

 shoots from near where these two stems divide. The Siricidae 

 also retain many highly primitive characters, although in otlier 

 respects "sidewise specialized". The Xiphydriidse, Cephidae, 

 and Megalodontidaj group themselves with them. The Oryssidae 

 represent the most highly modified group within the suborder. 

 They are more divergent from any other family than are any 

 of the other families from each other. Yet I believe they had 

 an ancestry somewlierc along the Sirieid stem. I am not con- 

 vinced of the taxonomic advisability of erecting super-faTiiilies 

 for small groups of their nature, representing as they do, 

 highly specialized offshoots of some other stock. 



The classification offered liy Dr. MacGillivray (1906) was 

 based upon careful and critical comparative study of a single 

 set of organs — the wings, and seems more conservative and 

 more in accordance with my own views. I have followed, in the 

 main, the arrangement which he proposes. 



I am not prepared, from personal knowledge, to offer an 

 o]iinion u]ion the advisability of dividing the Tenthredinida3 

 into several families, as is done by Ashmead and Rohwer. ft 

 is outside of the scope of this paper, and I have followed Dr. 

 MacGillivray 's classification in this regard. 



THE SUBORDER CHALASTOGASTRA 



A Key to the Families 



A. Front wings with R, present, possessing three marginal cells. 



XYELIDyE 



AA. Front wings with R, absent, therefore possessing one or two but 

 never three marginal cells. 



B. Front wings with subcosta present as a distinct longitudinal 

 vein. PAMPHILIID^ 



BB. Front wings with subcosta absent. (Rarely it is present as a 

 pale, very indistinct line, closely appressed to R -f M, or 

 SCj may be present as a transverse vein) . 



