1918.] Baini Prasiiad : The Anatomy of Aqifatic Diptera. 155 



terior margin fringed with minute hairs. Further back is the labrum. 

 (fig. 2), which is an elongated structure and has a large number of setae 

 arranged in a brush-like manner at its tip. The mandibles (fig. 3) are 

 large, plate-like, with a narrow base, and have six large teeth on their 

 anterior and upper margin and five small rounded serrations on the 

 inner ; besides there is near the upper margin on the outer side a small 

 projection with six very long and broad bristles arising from its surface. 

 The first pair of maxillae are reduced to small protuberances, each with 

 two setae at the tip, and the labium is only a very small plate. The 

 eyes are rather ovoid structures with a single large ocellus lying in a 

 depression on the posterior margin of the eye. The antennae are large 

 prehensile organs, consisting of a single joint; the line of attachment 

 to the head is nearly straight ; the outer margin of the antennae is con- 

 cave ; along the inner margin there is a deep notch close to the base, 

 beyond which the line is straight ; the tip is armed with four very long 

 bristles. A few scattered setae are to be seen on the clypeus and just 

 behind the eyes. 



The thorax is a fairly massive structure ; in full grown specimens it is 

 thrice as broad as the head. On the dorsal surface of the thorax there 

 are three groups of setae on each side ; the first or the prothoracic group 

 has two plumed setae, the second a simple and three plumed and the 

 third only three plumed ones. The air-sacs are more or less kidney- 

 shaped with the pigment arranged in small triangular or squarish areas ; 

 they are rather small as compared with those of the common Eurojiean 

 and American forms, bemg about one-sixth of the total thoracic length. 



The abdomen consists of nine segments. The first six segments 

 increase regularly in length and breadth, and the seventh and eighth 

 gradually taper to the ninth segment. Each of the segments I — \ III 

 bears a single plumed seta on each side dorsally and two plumed setae 

 ventrally. The air-sacs on the seventh segment are, like those of the 

 thorax, of a comparatively small size. The ninth segment has, close to 

 its base, a papilla in the mid-dorsal line with two setae arising from it ; 

 posterior to it are two more papillae but without any setae ; ventrally 

 there is the large fin formed of nineteen long fringed bristles of the same 

 type as described by Miall, op. cit. At the tip of the abdomen (fig. 4) 

 there are four small triangular gills close to the anus. Above the 

 gills are four very long feathered bristles arising in groups of two ; below 

 the gills is a large area something like the abdominal feet of Chironomiis, 

 and covered like these with two kinds of hooks (fig. 5), which are arranged, 

 the larger and slightly curved ones in the centre and the smaller and 

 more curved ones at the edges. 



Pupa of CHAOnoRUS ]\iantlensis. 



A point in which the habits of these pupae differed from those of 

 Palaearctic species was that they did not rise to the surface but remained 

 floating in a vertical position close to the bottom ; the large baloon- 

 shaped breathing trumpets keeping them in this attitude. The very 

 minute openings of the breathing trumpets, to be described later, seem 

 to be due to the peculiar habitat in which they live, as finely powdered 

 mud would choke up open trumpets, there being no large setae to guard 



