345] LARVAE OF THE TENTHREDINOIDEA—YUASA 27 



Subanal Lobe. — The membranous lobe (sbl) which forms the ventral 

 wall of the anal slit may represent the rudiment of the ventral half of the 

 ultimate segment or "telson." It is never distinctly chitinized, always 

 indistinguishably fused with the tenth abdominal sternum, usually setifer- 

 ous, and is rather restricted in extent. In the Tenthredinidae the subanal 

 lobe is strongly convex and extends to the anal larvapods, the postpedes of 

 Crampton. If the subanal lobe represents a part of the telson, and if the 

 subanal appendages (sba) of the Pamphiliidae and Cephidae are the 

 appendages of the ultimate segment, then the subanal lobe possesses a 

 pair of genuine appendages. In the larvae of the Xyelidae there occur 

 sometimes distinct subglobose setiferous swellings dorso-caudad of the anal 

 larvapods. Their homology and function are unknown. 



Tenth Urosternum. — The sternum of the tenth abdominal segment is 

 restricted in extent, more or less convex, and often glabrous. In the 

 Xyelidae and Tenthredinidae the anal larvapods occupy the greater part 

 of the caudal portion, which is thereby produced subconically ventrad. 

 This sternum is usually glabrous and more or less flattened in apodous 

 larvae. There are no annulations observable on this sternum. 



Suranal Process. — In boring larvae, the ultimate segment is provided 

 with a strongly chitinized mesal suranal process (srp) on the suranal lobe. 

 This process, which has been variously designated by different writers, is 

 characteristic of the families Cephidae (Figs. 108, 109, 112, 114, 115) 

 Xiphydriidae (Figs. 107, 110), and Siricidae (Figs. 113, 120, 122). The 

 size, shape, number, and arrangement of the dentiform tubercles and 

 setae vary in different families but they are constant within species and 

 often also within genera. It is undoubtedly an adaptive structure devel- 

 oped in connection with the boring habit of the larvae. It is interesting to 

 note that in some of the gall-making larvae of Pontania and leaf-stem 

 boring larvae of Caulocampus, the tergum of the ultimate segment is 

 produced on the caudo-meson and forms a distinct protuberance provided 

 with chitinized points on its caudal end. The larvae of the Pamphiliidae 

 also possess a minute hook-like process on the caudo-meson of the ultimate 

 tergum. The genetic connection of this hook-like tubercle and the distinct 

 suranal process of highly specialized families is doubtful, but it is not difficult 

 to surmise a common origin for the suranal process of the Cephidae, 

 Xiphydriidae, and Siricidae. The suranal process corresponds to the 

 postcornu of Crampton. 



Caudal Protuberances. — In certain genera of the Nematinae and in 

 a few other genera of the Tenthredinidae, the tergum of the ultimate 

 segment is provided with two or more protuberances which vary in size, 

 shape, number, and position in different genera. A typical condition in 

 nematid larvae is found in Pteronidea (Figs. 126, 127), which possess a 

 pair of conical, pointed, well-chintinized processes (srp), one on each side, 



