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ILLINOIS BIOLOGICAL MONOGRAPHS 



1452 



presence of vestigial clawless thoracic legs in the last three families, and 

 by the presence of either subanal appendages or suranal process or both. 

 The second subgroup contains a single family, Oryssidae, which is charac- 

 terized by the absence of both thoracic and abdominal legs, suranal 



Pbylogenetic tree indicating the probable affinities of various families of the Tenthredinoidea 



process, subanal appendages, and segmented maxillary and labial palpi. 

 The Xyelidae and Pamphiliidae are undoubtedly the most primitive of the 

 first and second groups respectively. 



The Tenthredinoidea, therefore, is considered to have developed 

 from a common ancestral stock along two distinct lines of evolution. 

 The first line of development led to the evolution of the Xyelidae and 

 Tenthredinidae and the second line produced the Pamphiliidae, Cephidae, 

 Xiphydriidae, Siricidae, and Oryssidae. 



