1918.] Baini Prasiiad : The Anntomy of Aqiiafic Diytera. 157 



a stout curved bristle hanging freely forwards. Internally the apex of 

 the margin, which in the natural position faces that of the mandible of 

 the other side, bears a large fringe of setae arranged on a crescentic 

 ridge a little behind the edge ; these setae together with the feeding 

 brushes of the labrum are constantly in motion and sweep the food 

 particles into the buccal cavity. A little above the middle there are two 

 large teeth while the lower half is finely serrated. The first pair of 

 maxiUae (fig. 11) are quadrangular in outline with a well developed 

 palp inserted near the base on the outer side ; the palp like the antennae 

 is spinose and of the same shape, though a little smaller. The inner 

 margin of the plate of the maxillae is beset with long hairs, those at the 

 apex being specially well developed and curved. The second pair of 

 maxillae are united to form a triangular labium, which forms the floor 

 of the buccal cavity. 



The three segments constituting the thorax are cpiite distinct. Seen 

 from above the segments are rectangular in outline. The middle se<^- 

 ment is the largest of the three. The first segment has five simple setae 

 on each side, arising near the anterior edge, and a single one behind 

 this group. The second bears laterally two setae on each side ; the 

 third has no setae. 



The eight segments of the abdomen are quite distinct. The first and 

 second segments are peculiar in having two small feet, one on each side ; 

 these feet bear two types of hooks, the arrangement of which is the same 

 as those described in Chaoborus, the larger ones in the centre and the 

 smaller ones along the edges. The second to the seventh abdominal 

 segments bear the so-called " shields " (Miall, op. cit.) on their dorsal 

 surface. These are only the dorsal surfaces of the segments marked 

 ofF as ovoid or nearly circular structures by the setae arranged alono- 

 their margins. The setae are both simple and plumose, and are 

 of use in supporting the surface-films of water, when in the looping 

 movements the larva brings it above the surface. The absence of these 

 shields in certain other species of Dixa larva suggests that they, together 

 with the setae, may be efhcient suckers of use to larvae living in rapid 

 torrents in the hills, but I have no definite facts to support this assertion. 

 On the ventral surface of segments five to seven there is, in addition 

 to the shields mentioned above, a comb-shaped structure formed of 

 minute brown spines attached in a transverse axis near the posterior 

 margin of the segments. The structure of the eighth segment is 

 very peculiar, having special bearings on the relationships of Dixa, 

 and has, so far as I know, not been adequately described for any 

 species. The segment itself is very large, the basal part being rec- 

 tangular, with an elongated conical portion of a brownish colour 

 projecting from the basal part. The tip of this conical portion bears 

 three long setae on each side. On the two sides, and arising from 

 the hind edge of the rectangular portion, are two triangular chitinous 

 plates of a dark brown colour ; these will be referred to again in the 

 account of the respiratory or breathing portion. With each of these 

 plates a rather elongated ovoid fin of a dark brown colour articulates ; 

 both the plates and the fins have a fringe of long setae along the inner 

 and outer margins. 



