268 GNATS OR MOSQUITOES — CHAPTER XI 



9. M. immisericors, Walker. Thorax inetallic-green ; scales on 

 costa blackish. 



10. M. Christophi, Portschinsky. Thorax black with inetallic-blue 



scales. 



11. M. Gilcsii, Theob. Thorax chocolate-coloured, with a greenish 



lustre. 



12. M. rxitilla, Coquillett. Thorax brown with golden and violet 



scales and pale yellow margins. 



C. Caudal tufts steel-blue and white. 



I. The tarsi with certain joints or bands whitish. 



13. M. Portoricensis, Von Riider. Thorax bay, with green-gold 



scales. 



D. Caudal tufts showing no contrasted colours, or not obviously present. 



I. Tarsi with certain bands or joints whitish. 



14. M. Amboinensis,Do\e&c\\al\. Thorax dark with glittermg golden 



scales ; abdomen steel-blue. 



15. M. trichopi/ga (Wied.) Thorax black with greenish-golden 



scales ; abdomen brown. 



16. M. ferox (Wied.) Thorax chestnut with azure median line ; 



abdomen steel-grey. 



II. With the tarsi uniformly coloured in the 3 ) adorned in the $ . 



17. M. longipes. No distinct caudal tufts. Thorax bronze and 



green-scaled. Abdomen pale olive-green. 



The characters on which the above table is based, and which 

 should, therefore, be especially noted are : — 



(a) The colouration of the characteristic " caudal tufts." These 



consist of dense brushes of hairs on the sides of one or two 

 of the last abd. segs., which are often brilliantly coloured, 

 and may contrast in a striking manner with the similar, but 

 somewhat shorter, hairs that densely fringe the end of the 

 abdomen. 



(b) The presence and position, or absence of pale tarsal markings. 



In this genus, the tarsi are rarely banded, so that these 

 usually take the form of patches, and not of complete rings ; 

 owing to which, they are apt to be overlooked, unless both 

 sides of the legs are inspected. 



(c) The colouration of the thorax, in connection with which, as 



with all colour qualifications of these brilliantly iridescent 

 insects, it must be borne in mind that they are mostly of 

 the sort usually spoken of as " metallic," or in other words, 

 depend, not on pigment, or natural colour, but upon the 

 phenomenon known as the interference of light passing 

 through the thin plates of the scales, and which, therefore, 



