The Philippine journal of science. [Vol. 57, no. 1]

57, 4

Tokunaga: Chironomidae, IV

501

the paired premandibles, which are articulated to the special
projections of the labralike, each provided with a set of antagonistic muscles at its basal projections. The distal half of the
premandibles is thin, somewhat concave on the mesal aspect,
and dentated into three blunt teeth on its edge, as in Plate 2,
fig. 12. The membrane mesad of the premandibles is swollen
and spinous. On the cephalic region of the epipharynx there
is a U-shaped chitinization, which is formed by the fusion of
originally paired secondary chitinization of the membrane.
Along the arms of this U-shaped structure there are paired
groups of minute hooklets. These hooklets (Plate 2, fig. 11)
are hyaline and flat, and those of the mesal side are finely serrated, while those of the lateral side are simple and slender.
On the cephalic margin of the epipharynx there are three minute,
hyaline, scalelike combs, which are finely and irregularly serrated on the distal margin. Besides these cuticular structures
there is a pair of brown thickened patches on the meson caudad
of the U-shaped sclerite or mesad of the premandibles.
The mandibles (Plate 2, figs. 8, 13, and 14) are symmetrical
in structure, comparatively slender, and each has two long sethe
on the ventrolateral surface. There are seven mandibular teeth.
The distadentis is somewhat slenderer than the proxadentes,
but there is no distinct differentiation between them. At the
base of the dental row is a strong hyaline seta. The brustia is
represented only by a proximal group of simple setae, which
are on the membranous area at the attachment of the retractotendon, and the number of setae is usually six. The extensotendon is slender, but the retractotendon is very large, thickly
chitinized, and oval.
The maxilla (Plate 2, fig. 8; Plate 3, figs. 16 and 17) is
membranous, connected with the ventrocephalic margin of the
vertex by the broad maxacoria, and consists of two chitinized
plates and two blunt distal membranous lobes. These two
sclerites are the cardo and the stipes. The stipes is reduced
into a small elongated sclerite on the dorsal side of the maxilla
at the base of the lateral membranous lobe, and the ventral
part of the stipes is reduced completely. The cardo is large,
located on the ventral side, and its mesal part is bent dorsolaterad. Thus, as the result of the reduction of the stipes, the
inner membranous lobe is directly supported by the semicircular
cardo at its base.