African Species of the Genus Cbiysops. 511 



Leopoldville, 1901; N'Kussu, Cataract Region, 25. xi. 1901 : 

 Drs. Button, Todd, ^ Cliristij) ; other specimens from Old 

 Calabar, Southern Nif!;cria {the late Miss M. H. Kingsley) ; 

 Ohumbele, Southern Nigeria, 0. viii. 1900 {Dr. H. E. Annett) ; 

 Odut and Uwet, May 1906 {G. C. Dudyeon) ; Sapele, 

 Northern Nigeria, 190G {received from Dr. G. F. Darker) ; 

 Akwatcha, Bassa Province, Northern Nigeria, July 1906, 

 January and February 1907 (Dr. G. J. Pine). According 

 to Dr. Piric C. silacea is numerous at Akwatcha in the dry 

 season ; and at Sapele, in Northern Nigeria, it is stated by 

 Dr. Darker to be troublesome to human beings. 



This species must not be confused with Chrysups diniidiata, 

 V. d. Wulp, the wing-markings of which are identical witli 

 those of C. silacea, while the buff-yellow abdomen is also 

 adorned with two black longitudinal stripes. C dimidiata 

 may be distinguished by the considerably larger and more 

 prominent frontal tubercle, which is only narrowly separated 

 from the eye on each side ; by the paler (buff-yellow) ground- 

 colour of the abdomen ; and by the fact that the abdominal 

 stripes are much broader and reach the fourth segment, when 

 they cither become merged in the dark brown colour of the 

 terminal segments, as stated by van dcr Wulp, or meet to- 

 gether on the sixth segment so as to form a loop. In C. silacea 

 the black stripes are sometimes so attenuated or interrupted 

 as to be easily overlooked, and in the case of one specimen 

 from Odut, Southern Nigeria, little more of them remains 

 than a couple of small dark flecks on the hind margin 

 of the first segment, and one or two indistinct markings 

 on the second. 



The range of C. dimidiata, which was described (' Notes 

 from the Leyden Museum,' vii. 1885, p. 80) from Chimhrao, 

 Portuguese West Africa, evidently overlaps that of C. silacea, 

 since the Museum possesses a series of specimens of the 

 former species from Ologbo, Southern Nigeria, May 1906 

 (G. C. Dudgeon). 



Eye-markinys *. — In two specimens from Sapele, pre- 

 served in spirit, the occipital border is fairly broad, and in 

 contact with the occipital margin and with the upper frontal 

 spot, which is also connected with the frontal margin. The 

 occipital border is also in contact with the shaft aijove and 

 the arrow-head below, which are continuous with each other, 



* For explanation of terms used see V. A. E. Dnecke's interesting 

 paper, " On the Eve-t\)loration of the Cieuus Chrysops " (' Eutoniulogical 

 IS'ews,' vol. xvii. lUOO, y\). 3!)-4l>, \>\. \.). 



