24 ILLINOIS BIOLOGICAL MONOGRAPHS (342 



The coxa {ex) is usually the largest of all the segments, subcorneal, and 

 articulated to the ventro-lateral margin of the segment. The cephalo- 

 dorsal angle is strongly chitinized and articulates against the chitinized 

 end of the episternum-epimeron. There is a distinct oblique depression 

 extending from this angle to the middle of the dorso-distal margin of the 

 coxa. The distal ends of the coxae are usually chitinized and form ring- 

 like thickenings. The ventral half of the coxa is more or less mem- 

 branous. The trochanter {tr) is usually small, longer on the ventral 

 than on the dorsal aspect. The femur (Jm) is usually cylindrical and is 

 often dilated at the distal end. Its ventro-distal portion is usually mem- 

 branous and is sometimes produced, forming a pointed projection, the 

 femoral process (Jp), as in Dolerinae (Fig. 135) and in related subfamilies. 

 The tibia {t) is subcylindrical, narrower in diameter at the distal than at the 

 proximal end, and either longer or shorter, than the femur or subequal to it. 

 The distal segment is typically very short and claw-like. The apparent 

 claw {cw) represents a fusion of the tarsus and tarsal claw, and is usually 

 sharp and distinctly curved. The segments are usually setiferous and 

 more or less membranous on the ventral aspect and at the joints. 



The general plan of structure of the legs is the same in a majority 

 of the larvae, but there are variations in the shape, size, arrangement of 

 setae, and in the number of apparent segments within the families and 

 subfamilies. The variations usually consist in the suppression of the 

 trochanter as in Phlebatrophia (Fig. 136) and the Fenusinae (Fig. 140), 

 or in the modification of the distal segment as in the Pamphiliidae (Fig. 130) 

 and Hylotominae, or in the reduction of the entire structure to a fleshy, 

 subconical, indistinctly segmented clawless protuberance as in Phleba- 

 trophia and certain highly specialized families. The absolute homology of 

 the segments in a modified leg can not be established, but when the number 

 of the segments is less than five it is probable that the trochanter is the 

 first one to disappear. 



The Pamphiliidae are distinct from all other tenthredinoid larvae in 

 having setaceous legs with all segments cylindrical except the distal ones. 

 The distal segment is very slender, non-setiferous, straight, and sharply 

 pointed without indication of a claw. The Xyelidae (Fig. 131) possess 

 legs which are small but typical in structure and number of segments. 

 It is quite possible to derive the normal tenthredinid legs from those of the 

 Xyelidae. In the subfamilies of the Tenthredinidae, a series of modifica- 

 tions of the legs is found, altho the majority of the subfamilies and genera 

 are provided with typical five-segmented, well-developed claw-bearing 

 legs. The Phyllotominae (Figs. 141, 142) are characterized by very 

 short, stubby, chitinized legs which consist of four segments, including the 

 large strongly curved claw. Phlebatrophia (Fig. 136) is unique among the 

 Tenthredinidae in having fleshy, rudimentary clawless legs. The Fenusi- 



