notch in the middle. The upper surface of the labrum is convex and 

 sclerotized, the lower surface concave and soft; the dorsal sclerotization 

 is either complete or incomplete, so that the anterior corners or the whole 

 anterior margin are membranous; in the Philopotamidae the greater part 

 of the dorsal surface of the labrum is soft and there is only a small 

 sclerotized part in the middle near the base. The posterior corners of the 

 dorsal sclerite of the labrum continue into narrow curved plates which 

 extend ventrad and are called tormae. 

 16 The labrum bears 6 primary setae: 3 lateral (l, 2, 3) and 3 on the surface 

 (4, 5, 6) (Figure 5);* seta 1 is situated at the sides of the median notch; 

 seta 3 is the longest of the marginal setae and is displaced toward the 

 lateral part of the labrum; the position of seta 6 as shown in the figure is 

 rather constant; seta 5 is usually longer than seta 6 and is situated lateral to 

 seta 6. Setae 1, 2 and 4 often have the form of light spines; the sides of 

 the dorsal sclerite bear 2 light pits which are not always distinct; there is 

 a well-marked pit in the middle of the sclerite. ** On the outer side 

 anteriorly and ventrally, the membranous surface of the labrum is covered 

 with soft, light hairs which are visible at the margin also in dorsal view. 



The musculature of the labrum consists of small constrictions originating 

 on the dorsal sclerite and inserted on its ventral wall. Two pairs of strong 

 rquscles, attached to the frontal sclerite, originate in the middle of the 

 endolabium and on the tormae. In some predators among the Annulipalpia, 

 the labrum may be retracted beneath the clypeus, enabling the mandibles 

 which are projected far anteriorly to catch the prey. 



The lateral sclerites of the cranium (Figure 3) bear 12 primary setae, 

 mainly on the dorsal, partly also on the dorsolateral surface of the head; 

 there are only 2 small ventral setae. There is a strong seta (No. 7) (after 

 seta 6 of labrus) near the anterior margin of the head, near the dorsal 

 articulation of the mandibles; this is usually longer than the intermediate 

 and median anterior-marginal setae or almost as long as these. The 

 large seta 9 is situated medially to the anterior margin of the eye; the 

 small thin seta 11 is situated posteriorly to it. The small seta 10 is 

 situated externally, near the anterior margin of the peri- ocular spot; the 

 short or moderately long seta 12 is posterior and lateral to the eye. The 

 large and stout seta 14, which is usually the longest seta of the head, is 

 situated more medially; (this seta is rarely short;) among the above setae 

 or near one of them is seta 13, which is small and thin and usually light; 

 setae 15 and 16 are situated in the posterior part. They are situated close 

 to each other or one behind the other; seta 16 is often short, curved inward, 

 sometimes recumbent; in the suborder Integripalpia, seta 15 is often long, 

 sometimes almost as long as seta 14; seta 17 is situated lateral to the 

 bifurcation, in the corner between the coronal and frontal sutures; this is 

 usually a small seta which sometimes (in some Hydroptilidae and in the 

 Brachycentridae) is one of the longest setae of the head. Ventrally, near 

 the lower articulation of the mandibles the short seta 8 is situated; the 

 small seta 18 is situated on each side of the gular suture. 



Differences in the form of the head are reflected in the distribution of 

 the setae of the parietal sclerites. In larvae whose head is concealed 

 under the overhanging anterior margin of the pronotum (while the eyes 



* The setae are numbered after Nielsen (1942:273—275, 278). 

 ** There is never a seta in this always distinct pit, although such a seta was sometimes erroneously described; 

 further details on such mistakes are found in Nielsen (1942:278). 



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