BY VERA IRWIX .SJIITII. 517 



l)luntly roiindeil tij). Tlu' lateral lohfs are situated some ilistaiice tuvtlier back, 

 0.15 mm. behind the median process. They are short, broad, rounded "bosses," 

 with rugose surface, composed of thick, dark chitin. Behind them, in the pos- 

 terior third of the head, there is, in the clear', membranous area on each side, a 

 prominent eye-swelling, bounded by a semi-circular membrane. The greater part 

 of the upper surface of the head is covered by a broad sclerite, presenting an 

 irregular series of transverse ridges, with two specially prominent ones on each 

 side (PI. xxvii., fig. 1). In front of each of these is a small bristle. Another 

 very small bristle is situated on each side of the median process. At the base of 

 the eye-swelling on both dorsal and ventral sides is a stout prominent hair, 

 about 0.32 mm. long. The ventral hair is accompanied by another very small 

 one. Two smaller bristles, of unequal lengih, are situated in front of them, 

 close to the ventral base of the lateral "boss." On either side of the mid- ven- 

 tral line, on a level with the lateral "bosses," is another small bristle, and a 

 similar pair is situated further back, towards the base of the head. There are, 

 thus, six pairs of Ijristles on the ventral surface, and four jDairs on the doi-sal 

 surface. All the bri.stles appear to he sensory in character, but none of them 

 correspond to the jointed antennae which are said to be present on the heads of 

 Stratiomyid larvae. If true antennae exist I have not been able to detect them. 

 In the figure whicli Brauer gives of a Sargus larval head, he marks the lateral 

 lobe "Fuhler," but in the Metoponia head this is clearly a portion of the chitinous 

 skeleton. However, there is, on the ventral base of each lateral lobe, a curious struc- 

 ture having much the appearance of a spiracle. It is in the form of a shallow, 

 cup-shaped projection, with a row of tooth-like processes projecting from its 

 inner margin, into its cavity (PI. xxvii., fig. 2) . 



The mouth parts are small, and dilfleult to distinguish, on account of the 

 dark colour and density of this part of the chitinous skeleton. They consist of 

 the median process, which probably corresponds with the structure called by 

 Becker (1910) the upper lip, and two pairs of small, pointed scale-like processes 

 lying close against its under side (PI. xxvii., fig. 2). The two inner processes 

 arc bent over towards each other at the tip, and so are somewhat hook-shajsed ; the 

 outer are sharply ]5ointed. In structure and arrangement, these mouth parts 

 differ considerably from those described by Becker and others for Stratiomyid 

 larvae, and will be considered more fully in a later paper. 



Stigmata. — The two prothoracic spiracles, situated close to the lateral mar- 

 gins of the segment, are large and prominent, dark brown in colour, and slightly 

 salient. They appear to be exactly similar to those of Patliygaster minutissima, 

 as described by Tragardh (1914). Two narrow oval slits open on a flat surface, 

 with a regular rounded outline, below which lies a larger area of chitin, of dis- 

 tinctive shape, shown in Text-fig. 14. A pair of very small spiracles is situ- 

 ated on the meta-thoracic and the first to the seventh abdominal segments, in the 

 lateral grooves, a little in front of the middle of the segment. They are of 

 simple structure, having a triangular aperture, bounded Ijy a dark brown circular 

 area (Text-fig. 9) . The two main tracheal trunks terminate internally, in the 

 last segment, in large spiracles, which open into a median pear-shaped air 

 chamber. This communicates with the exterior by a narrow aperture with 

 chitinous lips, situated at the bottom of the deep transverse split at the posterior 

 end (Text-fig. 15). If the supposition that a twelfth segment is really present, 

 is correct, this split would represent the dorsal incisure between the eleventh and 



