114 ILLINOIS BIOLOGICAL MONOGRAPHS [432 



Dr. Felt (1906) also found another larva making moderately large 

 cylindrical burrows in decaying birch and considered it as probably 

 belonging to X. attenuata. He refers to the rearing of this species by 

 Patton and suggests Rhyssa humida Say as its parasite. Since the identity 

 of Patton's specimen is questioned and since the adult was apparently 

 not reared, it is not possible to identify the specimen under consideration. 

 If it were really X. attenuata, then it should be known as X. abdominalis 

 as proposed by Konow (1905) and Rohwer (1918). 



Family Siricidae 



Body large, 30-40 mm., cylindrical, uniform in diameter thruout 

 (Fig. 4), fleshy, plump; integument smooth, transparent, non-setaceous, 

 light in color; head circular, half as high as thorax; mouth directed ventrad, 

 mostly exposed, but slightly overlapped by prothorax; antennae incon- 

 spicuous, apparently one-segmented; ocellarae wanting; epicranial suture 

 wanting and vertical furrow indistinct; mouth-parts not normal in form, 

 light in color; prothorax large; mesothorax and metathorax short in 

 comparison with abdominal segments; legs rudimentary, mamma-like, 

 subequal in size, borne on fleshy conical lobes; larvapods wanting; typical 

 segment with two indistinct annulets, sublateral lobe distinct but not 

 prominent; tenth abdominal segment semiglobose in profile; tenth tergum 

 distinctly depressed by a median furrow; suranal lobe on the meson with 

 dark colored, chitinized, suranal process; subanal appendages wanting; in- 

 ternal-feeder, bores in the trunks of deciduous and evergreen trees. 



The Siricidae contains five genera and about fifty species, most of 

 which are confined to the northern hemisphere. The recognition of the 

 fact that these insects constitute a well-circumscribed group dates back 

 to the time of Linnaeus (1758) who described five species of Siricidae among 

 those of his heterogeneous genus Ichneumon, three of the five having 

 become the types of three modern genera. Systematists have universally 

 agreed in considering this group worthy of family rank. The family 

 falls into two natural divisions, Siricinae, including three genera, Sirex, 

 Urocerous, and Xeris, and Tremecinae, embracing two genera, Tremex 

 and Teredon. The genus Xeris was associated with the genera composing 

 the Tremecinae both by Ashmead (1898) and Konow (1905), but Rohwer 

 (1911) proposed a more natural arrangement, placing this genus in the 

 Siricinae. Bradley (1913) definitely divided the two groups on the number 

 of segments of labial palpi and the retention of cerci in the adults. 



According to Bradley (1913) there are twenty species reported for 

 North America, representing all the known genera. The specific charac- 

 ters of some common species, as Sirex nigricornis, Urocerus cressoni, and 

 Tremex columba, are subject to a wide range of variation and several 

 varieties have been described. So far as known, the larvae of the Siricinae 



