68 THE REPORT OF THE No. 36 



reduced to a narrow, connected band forming a continuous mark across the 

 lateral and cephalic aspects of the head. Larv« marked in this way usually 

 hold the head so that the black line coincides with the cut edge of the leaf. The 

 second clypeus and labrum are usually of the same color as the head. In the 

 black-headed species they are sometimes lighter or entirely pale. 



The head is usually very pale in color immediately after moulting. If the 

 head is normally green or white in color, this is not noticeable, hut in the black 

 or brown headed species it is strikingly so. In the Tenthredininse, while some of 

 the species have the head entirely green or white throughout their life, most of 

 those studied had one or more black spots. These were located on the vertex, 

 front, or genge. Although usually coal black in color, they completely disappeared 

 during the ultimate stage and the head became glassy green in color. 



The region behind the head consists of thirteen segments, the cephalic three 

 (Fig. 1, tl-3) belong to the thorax and the caudal ten to the abdomen (Fig. 1. 

 al-10). The thoracic segments are frequently more robust than the abdominal 

 segments, while the tenth abdominal segment is quite different in shape from 

 the others. 



The thorax, while apparently consisting of three parts, is in reality a com- 

 pound of four. The microthorax (Figs. 1 and 27, mc), the so-called neck, which 

 is the segment bearing the labium, forms the cephalic part of the first segment 

 of the true thorax. The folds of cuticle between the head and thorax conceal 

 the microthorax for the most part, it shows as a darker colored V-shaped area 

 along the cephalic part of the ventral margin of the lateral aspect of the pro- 

 thorax and is closely associated at its cephalic end with the labium. Similar V- 

 shaped areas are found in practically all tenthredinoid larvse, as Croesus^ Pter- 

 anus, Lyga'onematus, Ahia, and Lophyrus. This area is reduced to a protuber- 

 ance in Cimbex, to a slight brownish mark in Cephus, and is completely wanting 

 in Tremex. (Fig. 10). In larvae containing black or fuscous markings, this area 

 of the microthorax (Fig. 27, mc) is almost invariably so marked. 



The three sub-regions of the thorax can usually be identified by the presence 

 of thoracic legs. This is true in the Xyelidae, Pamphiliidae, and Tenthredinidge. Iii 

 the remaining families the thoracic legs are generally represented by short, un- 

 segmented stiibs or swellings (Fig. 10, tl). The mesothorax and metathorax are 

 similar in form, the prothorax resembles them closely, but in many species, par- 

 ticularly among the Tenthredinidse, the thorax is greater in diameter than the 

 head, and the dorsal portion of the prothorax is declivous. Among most larvse 

 other than the Tenthredinoid ea, it is quite characteristic for them to have a trans- 

 verse plate on the dorsal aspect of the prothorax and sometimes even on the other 

 subdivisions of the thorax, such a chitinized plate or dorsal shield is found in the 

 Tenthredinoidea only in the family Pamphiliidae (Fig. 1, d), where it appears to 

 be characteristic of all the species. In some species this plate is divided into three; 

 parts. The segments of the abdomen as already indicated are quite similar in 

 form to each other except the tenth (Figs. 1, and 27), which will be discussed 

 more fully later. 



The external openings of the respiratory system, the spiracles (Fig. 1, s), are 

 usually distinct and frequently surrounded by a different color from the adjacent 

 parts of the body. There is a pair of spiracles on the prothorax, located near its 

 caudal part in Pamphilius, and near the middle of the segment in the Tenthvedinidae 

 (Fig. 27). These spiracles are morphologically the mesothoraeic spiracles, which 

 have migrated from their position hetween the segments on to the prothorax. They 



