248 SYRPHID.E. 



much l)roader than the first ; tliird flat, almost circular ; fourth very 

 minute, seated near the base of the third; ffth setiform, bare or 

 pubescent. Thorax subquadrate, pubescent. Bcutellnm somewhat 

 convex, with an undefined edge, semicircular. Wings lanceolate, very 

 finely pubescent, diverging ; siibajjical areolet entire, narrowed in 

 the middle ; axillary lobe distinct, sid)costal and radial veins ending 

 separately in the margin ; transverse prabrachial vein placed beyond the 

 middle of the discal areolet ; alulfe large, double. Halteres covered. 

 Abdomen elliptical, obconical, or linear. Hind femora long, fusiform, 

 thicker than the anterior, beset with spines beneath towards the tips ; 

 hind tibia) curved. Afale. Eyes more approximate than in the female. 



The larvae of some species of this and of the preceding genus 

 are aquatic, and their structure and habits are described in the 

 following extract : — " The larva of Helop/dlus penduliis has four- 

 teen unguiferous prolegs or tubercular, which are perhaps con- 

 nected with the respiration ; they are affixed by pairs to the ven- 

 tral segments, the twelve posterior ones of which are subconical, 

 and truncate at the apex, which is surrounded with two circles of 

 very minute claws, those of the inner being much more numerous 

 and shorter than those of the exterior circle ; while the anterior 

 pair terminate in a flat expansion, and in shape almost exactly 

 resemble those of a mole. When about to assume the pupa-state, 

 it leaves the water and betakes itself to the shore, and resides in 

 the earth. The respiratory organ is a continuation of the tail, 

 and is composed of two tubes, the inner one, like the tube of a 

 telescope, being retractile vin'thin the other. The extremity, which 

 is very slender, and through which the air finds admission by a 

 pair of spiracles, terminates in five diverging hairs or rays, which 

 probably maintain it in equilibrium at its station at the surface. 

 As these larvaj seek their food amongst the mud at the bottom of 

 shallow pools, in which they are constantly employed, they require 

 an apparatus capable of being lengthened or shortened, to suit 

 the depth of the water, that they may maintain their necessary 

 communication with the atmosphere; and therefore, both these 

 tubes are extremely elastic, consisting of annular fibres, so as to 

 admit their being stretched to near twelve times the length of the 

 animal. The mechanism by which the terminal piece is pushed 

 forth or retracted, consists of two large parallel tracheae ; the di- 

 rection of these is from the head of the grub to the tail, and they 

 occupy a considerable portion of its interior : near the origin of 

 the tail, where they are very ample, they suddenly grow very small, 

 so as to form a pair of very slender tubes, but so long, that, in 

 order to find room in a very contracted space, they form nume- 



