S98 REPORT OF THE HARVARD AFRICAN EXPEDITION 
there are probably in the rain forest of the West African Subregion several closely 
allied, though distinct, species of this group. Three of them are found in the 
Belgian Congo and may, I believe, be separated by the characters given in the 
key. The true C. dimidiata has in my opinion been correctly figured by Austen 
(1909). It is probably widely distributed throughout West Africa; but, as it 
has certainly been often confused with C. silacea, its distribution cannot be given 
correctly at present. It is to be hoped that a serious effort will be made to clear 
up the status of the species belonging to this group, since it contains the carriers 
of an important human parasite, Loa loa (Guyot) (see above). 
Chrysops silacea Austen 
Chrysops silacea Austen, 1907, Ann. Mag. Nat. Hist., (7) XX, p. 509 (@; Kimuenza, Belgian 
Congo, one of the original localities, may be designated as the type locality); 1909, ‘Illustr. 
African Blood-Suck. Flies,’ p. 48, Pl. II, fig. 15 (¢). J. Bequaert, 1913, Rev. Zool. Afric., I, 
3, p. 221 (9), fig. 2 (eye 9; wrongly labelled dimidiata). Kréber, 1927, Zool. Jahrb., Abt. 
Syst., LITI, pp. 181, 185, and 218, Pl. V, fig. 14 (¢). 
BELGIAN Conco. — Bafwankei (between Bomili and Avakubi), December 
29, 1913. Yakuluku; Nala; Duru; Rungu; Boyo; Gombari; Atede (all 
localities in the Uele District) (J. Rodhain). Medje; Akenge (H. Lang and 
J. P. Chapin). 
This species is undoubtedly much more common than the closely allied C. 
dimidiata, although it probably has the same general distribution. It is known 
at present with certainty from the Gold Coast, Southern and Northern Nigeria, 
Cameroon, Fernando Po, Spanish Guinea, the Gaboon, and the Belgian Congo. 
Chrysops centurionis Austen (1911, Bull. Ent. Res., II, p. 164, fig. 2; 9; 
Buanaka, Chagwe, Uganda) is very close to C. stlacea and Kroéber (1927) regards 
it as only a color variant of that species. The characters which Kréber uses in 
his key (1927, p. 185) to separate silacea and centurionis are only partly correct. 
In these two forms the color of the wings is the same, as figured by Kroéber in 
his Pl. III, fig. 18. Kréber’s fig. 19 of the same plate, labelled ‘‘centurionis Aust. 
¢ (nach Austen)’’ has nothing to do with that species and seems to be a mere 
fantasy. On p. 221, however, Krober states correctly that the whole distinction 
is in the striping of the thorax: in szlacea the two median chrome-yellow stripes 
of the dorsum are continuous; in centurtonis they are described by Austen as 
‘a pair of more or less faint and indistinct chrome-yellow or buff-yellow admedian 
pollinose stripes, which, starting from front margin, disappear on or shortly 
before reaching transverse suture, and are again visible close to posterior margin, 
where they: curve round on to the postalar calli.’ This aspect may be merely 
due to the pollinosity being partly dulled or rubbed in certain specimens and, 
if no other differentiating characters can be found, I should synonymize centu- 
rionis with silacea. Attention is here called to this form, because it very likely 
will be found within the boundaries of the Belgian Congo. 
Chrysops langi, new species 
Female. — Length, 12.5 mm.; width of head, slightly under 4 mm.; width of frons at vertex, 
about 1 mm.; length of wing, 11 mm. 
A large, dark brown species, closely allied to C. dimidiata, with which it agrees structurally: 
v ? 
