132 ILLINOIS BIOLOGICAL MONOGRAPHS [450 



recognized the Pamphiliidae as the most generalized from his study (1913) 

 of the immature stages. Had he placed the Pamphiliidae before the 

 Xyelidae and the Cephidae before the Xiphydriidae and Siricidae, his 

 system would coincide exactly with the system based exclusively on the 

 immature stages. Konow and Rohwer both associate the Cephidae 

 with the Pamphiliidae and Xyelidae. This arrangement is partly supported 

 if the affinity between the Pamphiliidae and Cephidae, as suggested in 

 this study, is upheld. The genetic continuity of the Xyelidae and Ten- 

 thredinidae is clearly recognized by MacGillivray (1913). The true 

 systematic position of the Tenthredinidae or its equivalent is difficult 

 to express in linear arrangement. The important point to be noted is the 

 fact that these authors and also Morice (1919) consider the Xyelidae and 

 Tenthredinidae as different and apart from the other families of the 

 Tenthredinoidea. The Oryssidae unquestionably merits at least separate 

 family rank. In the absence of requisite knowledge of the larval characters 

 of the Hymenoptera other than the Tenthredinoidea, it is not expedient 

 to venture any opinion on the suggestion made by Rohwer and Cushman 

 (1917) to establish a third suborder, Idiogastra, for the reception of the 

 Oryssidae. Enslin (1911) differs from the authors already mentioned 

 not only in his arrangement of the groups in a descending order but also in 

 treating the Xyelidae and Pamphiliidae as subfamilies of his Tenthredini- 

 dae, on a level with the Cimbicini, Lophrini, and others. This study does 

 not support his arrangement. Morice (1919) suggested that "the Lydini 

 (Pamphiliidae Ensl.) may represent a primitive group of Tenthredinidae 

 which had branched off from the main stock before it had developed 

 certain characters," such as abdominal legs. Handlirsch (1908) considered 

 the Siricidae as having evolved from the osculant Juracic group, Pseudo- 

 siricidae. The antiquity of the Siricidae is accepted by Morice who 

 expresses his idea of the relationship of the families of the Tenthredinoidea 

 as follows: "We may suppose that the Siricidae are the earlier group, 

 but whether the Tenthredinidae and Lydini had Siricid ancestors, or 

 whether the Siricidae-f-Cephini-f-Oryssidae and Tenthredinidae+ Lydini 

 are respectively earlier and later branches of a common stock are questions 

 which must be left unanswered." 



