LAMB—DIPTERA: HETERONEURIDA, ORTALIDA, TRYPETIDA), SEPSIDA, ETC. 335 
and faintly ridged in a more or less longitudinal direction. Head bristles black and 
strong; front f. 0. pointing forward and outward and more remote from eye boundary 
than usual, the distance between their insertions being about half the frontal breadth at 
the corresponding cross line; hind f. o. about half-way between the front f. 0. and the 
i. v., pointing backwards; a continuing row of 6 or 7 small bristles to the forehead. 
Convergent i. v., divergent o. v.; p. v. on vertex behind ocelli, crossed half-way ; oc. 
inserted well beyond front ocellus (much in the position shown in Plate 20, fig. 22), 
divergent and stout. In this view the hind angles of eyes can be seen to project behind 
the head. Front view :—the head is very broad, about 24 times as broad as deep, owing 
to the projecting eyes. The face to the ridged mouth margin is pale with a definite though 
narrow central keel forming two antennal foveze: these are slightly darkened at the 
bottom. The clypeal edge is blackened ; palpi clubbed, black, and bristled ; tongue yellow 
and hairy. Side view (Plate 20, fig. 21):—antennze darkened grey, paler inside, the 
lighter third joint with white pubescence; second joint with four or five stout spines and 
smaller hairs. Arista stout, with the inner row of rays very marked and strong; upper 
row with about four straight rays at base, then three curved ones; lower row with one 
long straight ray below the upper, two or three curved ones, a terminal one. A pair of 
very stout vibrisse followed along the mouth edges by finer bristles. The hind jowls with 
three or four longer bristles. A well-marked post-oc. row. In this view the eyes are 
- much elongate, the hind facets are perceptibly smaller than those in front. 

Fig. 21. Drosophila aberrans, n. sp. x 30. 
Thorax. Brown with orange tone, dull: some sign of sparse paler pollination in 
front; two ill-defined narrow paler lines along the d. c. lines. The dorsum is covered 
with small bristles arranged in regular longitudinal lines. Only the last pair of true 
large d. c.: the fine bristles between the d. c. lines form 6-rowed acrostichals. The 
humeri bear some 3 or 4 somewhat prominent bristles round the edge. ‘Two n. p., presut., 
two b. over wing-base, two on alar callus, the inner smaller. The pleurze below the line 
from wing-base to point below humeral callus is more or less darkened: the sternopl. has 
one stout lower and two smaller upper bristles. Scutellum rounded, bare, dull, con- 
colorous with the thorax except for a slightly lighter tip and margins ; two stout basal, 
and two stout crossed terminal bristles. Wings, as Fig. 21, suffused, with brownish 
veins, the two cross veins being somewhat blackened; costa to 4th, no costal break, but 
1 or 2 spines there. Halters orange. Legs yellowish-white, bristled in rows, the under 
