coronal suture; they are contiguous along the medioventral hypocranial 

 (gular) suture. This suture extends from the occipital foramen to the gnathal 

 foramen; in some species, however, its anterior part branches in most 

 larvae into the gular sutures which enclose the gula. The gula extends in 

 some species from the gnathal foramen to the occipital foramen, separating 

 the lateral sclerites and gular sutures. The epicranial and hypocranial 

 sutures form narrow membranous spaces between the sclerites; 



In addition to the membranous sutures, there are also hard sutures which 

 form rigid connections between the sclerites. On the frontoclypeus, these 

 are the epistomal or clypeal suture, separating the frons from the clypeus. 

 A more or less distinct suture separates a narrow plate at the anterior 

 margin of the gula; this sclerite is the pregula, and is often fused with the 

 gula. The subgenal suture is a continuation of the pistomal suture; it runs 

 parallel to the gnathal foramen and delimits a narrow subgenal margin 

 which constitutes, together with clypeus and pregula, the anterior thickened 

 margin of the cranium with which the mouthparts are contiguous or articu- 

 14 lated: the labrum is attached to the clypeus, the mandibles and sclerites 

 of the cardo are attached to the subgenal surface, and the middle of the 

 submentum to the pregula. There is almost always a narrow ridge which 

 forms the posterior margin of the cranium near the occipital foramen. 



^W?% 



^ 



\ W!" 4 



FIGURES 3 and 4 



3 —head ofRhyacophila nubila, dorsal (A) and ventral (B); 4 — antenna of Wor 

 maldia occipitalis (after Nielsen). 



11 



