184 Memoirs of the Indian Museum. [Voi,. V, 



w 



At the distal end of the anterior tibia on its proximal side, there is in both sexes 

 a stout blunt process about as long as the segment is wide ; it fits into a groove on 

 the ventral surface of the femur when the two segments are approximated. On the 

 process we can find no trace in either sex of the " file" figured by Carpenter in his 

 account of Halobates herdmani ' ; but in the male, immediately in front of it at the 

 distal end of the segment, there is, as in that species, a group of slender spines, gradu- 

 ated in length. 



The external genitalia do not differ in any important respect from those of Halo- 

 bates. In the male (pi. xi, fig. 5) the horns of the eighth abdominal segment are sym- 

 metrical, reaching about to the middle of the ventral plate ; they taper regularly to 

 a blunt apex, which is slightly reflected outwards. Their distal ends are covered with 

 scattered thorns that extend farther forwards on the external surface than elsewhere. 

 Dorsally, on the posterior margin of the eighth segment, there is a large rounded promi- 

 nence and at each posterior angle there is a small papilla on which the spiracle opens. 

 The ventral plate is broadly oval, convex below. The sclerite of the ninth abdominal 

 segment is large and has the usual form; the postero-lateral margins are strongly 

 sinuous and on each side behind the lateral prominences there is a patch of about 

 twelve coarse spinules. We figure the female genitalia as seen from the side in an 

 extruded condition and also, as seen from above, when retracted (pi. xi, figs. 6, 7). 

 They resemble those of Halobates herdmani as figured by Carpenter (loc. cit.), but the 

 ovipositor (outer posterior gonapophysis) is longer and the inner branch of the ante- 

 rior appendage of larger size, while the posterior appendages extend much further 

 beyond the basal membrane. 



The egg is sausage-shaped and very long. One removed from the abdomen of a 

 female is i - 88 mm. in length and fully three times as long as broad. 



There appear to be three larval instars. In the first (pi. xi, fig. 1) the thoracic 

 and abdominal sclerites have not yet appeared, except that there is a small chitinous 

 plate at the extreme tip of the abdomen. The tarsus of the first leg is short and 

 relatively broad and is composed of a single segment. The first segment of the antenna 

 is also relatively short. 



In the next instar (pi. xi, fig. 2) the prothoracic sclerite is well developed, form- 

 ing a transverse bar interrupted in the middle line. On each side of the meso- 

 thorax there is a large longitudinally oval chitinous plate, while on the meta- thorax 

 there is a pair of much smaller obliquely transverse plates, widely separated in the 

 middle line. The tergites of the first five abdominal segments are represented by 

 small patches of chitin placed laterally on either side and decreasing in size from 

 before backwards. On the sixth and seventh segments these patches are scarcely 

 distinguishable, but on the eighth there is a pair of larger plates, round and approxi- 

 mated to one another. The apex of the abdomen is in the same condition as in 

 the former instar. The tarsus of the first leg has increased in length, but still con- 

 sists of a single segment; the femur bears a small projection on the lower surface at 



Carpenter, Ceylon Pearl Fisheries, V, plate, figs. 5-7 (1906). 



