BY G. H. HARDY. 187 



The exoskeleton jsIiows dififerenees oi specific value in the characters disciissed 

 below . 



Head. — On the face there is a tubercle varying in size in the different species, 

 and on this is situated the moustache which varies in density approximately in re- 

 lation to the size of the tubercle. N. claripes White, N. volaticus White, and iV. 

 aKstralis Ricardo have a very small tubercle and moustache, whilst the other spe- 

 cies have these characters generally much more pronounced. 



A row of bristles is situated behind the eyes in most of the species, but in a 

 few apparently undescribed forms they are absent. Some species have these 

 bristles arranged in two rows or more. 



Thorax. — The presutural bristles are those lateral bristles situatefl anterior 

 to the transverse suture; they are always two in number close to the suture, and 

 anterior to these there are sometimes one or more further bristles . 



The sviperalar bristles are those situated above the wing's, between the trans- 

 verse suture and the postalar callus. They may be one, two, or three in number, 

 rarely more. 



The postalar bristles are those situated on the postalar callus, and may he 

 from one to four in number. 



The dorsocentral bristles are confined to two rows on the dorsum placed on 

 each side of, at some little distance from, and parallel to the median line. 1 hese 

 bristles are usually regularly placed and alternate with a row of hairs placed in a 

 closely adjacent or a contiguous line; if one of the bristles is suppressed or 

 obsolete, the hair on each side of it becomes much stronger and bristle-like. When 

 counting, allowance must be made for these suppressed bristles, but sometimes 

 specimens will be found too irregular for the alternating hair and bristle character 

 to be seen. 



As these dorsal thoracic bristles appear to have a definite limit of variation 

 in each species, they afford important characters for identifying female specimens. 



The metapleural bristles are situated below the halteres ; these are erect and 

 are arranged in a vertical line. Below, above the hind coxae, and continuing in 

 the same line, are also erect hypopleural bristles. The metapleural bristles are 

 invariably present, but sometimes the hypopleural bristles are reduced to depi-cssed 

 hairs, or are completely missing. Both sets of bristles are very thin and hair- 

 like, but as they stand erect on an otherwise bare surface they are very con- 

 spicuous . 



Scutellmi. The seutellar bristles are situated on the margin of the seutellum, 

 and are from two to six, rarely more, in number. 



Abdomen. A row of bristles may be present on most of the abdominal seg- 

 ments. These bristles are generally in a complete line on the first segment, but 

 are interrupted bv a bare space on the dorsum of the other segments; they are 

 placed parallel and anterior to the posterior margins; they are smallest towards 

 the centre, and become longer laterally, where they are often erect and conspienous. 



Legs. The femur is more or less oval in cross section, and when the legs are 

 at right angles to the thorax, that flattened surface which faces towards the head 

 is known as the anterior side; the other three sides are called the dorsal, posterior 

 and ventral sides. 



The anterior femur is generally spineless, but occasionally a spine is to l)e 

 found towards the apex of the posterior side, and A^. armatus Macquart has four 

 spines on the ventral side. 



A complement of spines on the intermediate femur appears to consist of n 



