PSILOCEPHALA. 305 



244. Psilocephala sequa, Walk. (PI. III. figs. 17-20.) 



Thereva sequa, Walker, Ins. Saund., Dipt. pt. 1, p. 157 (1852). 

 <5 $ . Bead in c? with eyes contiguous for about half the distance 

 from fro us to vertex, leaving an elongate light yellowish-grey 

 vertex bearing a few brown hairs, with the front ocellus at some 

 distance from the other two ; ocelli red ; frons at level of antennae 

 nearly one-third of the head, and with face wholly covered with 

 snow-white tomentum, with here and there a little short con- 

 colorous soft pubescence ; upper corner of frons with a few black 

 stiff hairs. Proboscis short, thick, dark brown, extending as far 

 as tij) of 1st antennal joint, with moderately long soft white hairs. 

 Anteunal 1st joint blackish, white-dusted, with numerous strong 

 black bristles; 2nd and 3rd joints dull red-brown, with a little 

 greyish dust ; 2nd nearly cylindrical, with a few short bristles ; 

 3rd elongate, bare. Occiput projecting only slightly behind eyes, 

 covered with hoary tomentum, a little white pubescence, and some 

 strong black bristles. In $ , frons at vertex broader than in <S , 

 widening rapidly to level of antennae, where it is one-third the 

 width of the head ; eye-margins slightly emarginate towards 

 antennas ; the yellowish-grey colour of the vertex extending half- 

 way to antennae and on its lower margin overlapping the snow- 

 white frons, a large rounded or subtriangular black spot on each side 

 touching the eyes ; vertical margin with a row of about ten black 

 bristles. Thorax wholly covered with pale bluish-grey tomentum ; 

 dorsum darker, with two narrow well-separated whitish stripes 

 (the intermediate space often brown), running practically from 

 anterior to posterior margins ; dorsum covered with fine brownish 

 pubescence of some length, and sparsely with short snow-white 

 hairs ; thicker and longer whitish-grey pubescence on the pleurae 

 and underside between the first two pairs of coxae. Normal 

 macrochaetoe along sides of thorax, dorso-centrals represented by 

 a single pair near hind margin ; scutellum, which is clothed with 

 hoary tomentum and soft whitish pubescence, bearing four bristles, 

 a marginal and an apical pair. Abdomen in d covered with silvery- 

 white dust, which is most conspicuous seen from above, as, when 

 viewed from behind at a low angle, it almost disappears, the 

 abdomen seeming dusky; there being also some short snow-white 

 hairs, and at the sides much longer fine white or nearly white 

 pubescence, which has a tendency to form a fan-shaped bunch on 

 each segment, especially on the first three; venter blackish, nearly 

 bare; hind margins of 2nd, 3rd, and 4th segments distinctly 

 brownish yellow ; tip of abdomen with a few bristles ; geuitalia 

 reddish brown. In $, deep black, with microscopic depressed 

 yellow hairs ; 1st segment wholly grey-dusted ; towards sides of 

 each remaining segment a snow-white tomentose triangular spot 

 with short snow-white pubescence ; these spots being largest on 

 2nd and 3rd segments and smallest on 4th, on 5th and 6th 

 segments they are merged in a general whitish-grey dusting; 

 surface of abdomen with sparse long stiff black hairs from 4th 



