40 ILLINOIS BIOLOGICAL MONOGRAPHS [358 



abdominal segments including the first and ninth, where they are some- 

 times reduced in size; typical segments with four annulets; spiracles on the 

 second annulet; sublateral lobe produced ventrad, modified into a triangu- 

 lar lobe laterad of larvapod which it resembles in form; ninth abdominal 

 tergum with three annulets; tenth abdominal tergum constricted distinctly 

 and transversely on its cephalic fourth and with a distinct hump-like protu- 

 berance on the meson caudad of the cephalic constriction, concolorous with 

 the head and setiferous tuberlces; anal larvapods and ventral or subanal 

 lobes distinctly large, contiguous, forming a trilobate prominence on the 

 meson of the tenth sternum; subanal lobe with a pair of setiferous protu- 

 berances dorsad of larvapods; insects single-brooded, solitary, chiefly 

 exposed-feeders; pupate in earthen cells in the ground. 



The Xyelidae is a small family consisting of seven genera and of 

 a limited number of species, most of which belong to the North American 

 fauna. The adults are readily distinguished from all other Hymenop- 

 tera by the presence of the free part of the vein R2 in the wings. On 

 venational characters, MacGillivray (1906) considers the members of this 

 family to be the most generalized Hymenoptera known, having, "departed 

 from the type of the wing assumed for the original progenitor of the 

 Hymenoptera only in the loss of the free part of vein Cu2." The genera, 

 at the same time, possess many features of prominent progressive speciali- 

 zations which have proceeded in each case in a different sequence so that 

 a linear arrangement of the genera does not express their true affinities. 



Over twenty-five species have been reported from boreal America. 

 Of this number, four species belonging to as many genera have been recog- 

 nized in the larval state. Another unidentified species, feeding on pecan, 

 is added in this paper. Dyar (1898) described the larvae of Megaxyela 

 major and Xyela minor and gave a definition of the family based on charac- 

 ters found in these species. He pointed out that they are most nearly 

 related to the Pamphiliidae. The larvae of Odontophyes aviingrata were 

 described by the same author (1899). Konow (1901) overlooked Dyar's 

 1898 paper and gave in his analytical table for the larvae Odontophyes 

 aviingrata as the sole representative of the subfamily Xyelini. That 

 Konow was unfamiliar with any xyelid larvae may be reasonably assumed 

 from the fact that he classified them with those larvae which had no 

 larvapods and that he placed a question mark before the analytical item 

 "ohne Afterborsten." The larvae of Pleuroneura, Paraxyela and Proto- 

 xyela are unknown. The described larvae feed on the foliage of hickory, 

 butternut, pecan, elm, and the staminate flowers of pine. 



The most important materials that I had in the study of this family 

 were received from Professor R. W. Harned, of the Mississippi Agricultural 

 College, but, altogether, the material at hand is so limited that it does 



