Species of Simulium//-o??j the Siamese IJills. 587 



The anteniise are brown, yellowish white at the base. In 

 spirit the abdomen is white, with brown bands posteriorly, 

 lire legs are banded black and white ; the tarsi of the front 

 pair are much stronger than those of the other pairs. The 

 wings are hyaline. 



Head velvety black, with golden hairs between and 

 behind the eyes ; the face also is black. Antennce dark 

 brown, except the first two segments and a part of the third, 

 which are yellowish white. Palps brown, with the exception 

 of the second segment, which is black. 



Thorax velvety black ; the scutum is covered more or less 

 with bright golden hairs. 



Wings hyaline, with only the first and third longitudinal 

 veins distinct and dark. Ilalteres yellowish white. 



Legs. — Femora and tibise are white at the proximal end, 

 dark brown at the distal end. All the tarsal segments of the 

 first pair of legs are dark brown, but in the second and third 

 pairs the metatarsus is yellowMsh white in the proximal half, 

 and the next tarsal segment has a white spot at the base. 

 The penultimate tarsal segment is heart-shaped in all the 

 legs. 



Abdomen. — In spirit-specimens the first two segments are 

 white; the third, fourth, and fifth are white, each with a 

 dark brown dorsal cross-band ; the last two are entirely 

 brown, darker dorsally than ventrally. 



The mouth-parts seem to be similar to those of other 

 species. The second segment of the maxillary palps has a 

 curious little, probably sensory, vesicle, with a minute 

 circular opening on the side of the segment. 



SimuUum Jiigrogilvum is about the same size as Simulium 

 indicum, but it differs from that species in the following 

 points : — (1) The base of the antenna is yellowish white, 

 whereas in S. indicum the antennas are entirely dark ; (2) the 

 femora and tibiaB are half white^ half black, but in >S'. indicum 

 they are said to be black-brown ; (3) the first two segments 

 of tlie abdomen are white, and ventrally all the rest of the 

 abdomen except the tip is white also ; whereas in S. indicum 

 only the first segment and the sternal parts of the next three 

 segments are yellowish white. 



Simulium nigrogilvum. is much larger than SimuUum nohile, 

 which measures only 1'5 mm. The other points of difference 

 between the two species are as follows : — (1) The antennse of 

 8. nobile are reddish yellow, with black tip ; (2) the thorax 

 of S. noUle is said to be almost naked, with a silver-white 

 sheen, only a posterior strongly arched cross-band being 

 velvely black, whereas in S. nigrogilvum the scutum is 



39^ 



