affecting the Potato-crops. 109 



the crown : thorax globose-quadrate ; scutel semi-ovate : abdomen 

 small, depressed, oval, blackish, and 6-jointed, with 4 or 5 ochre- 

 ous bands ; the apex pointed in the female : wings incumbent in 

 repose, very long and ample, yellov^^ish and iridescent, with a 

 very short marginal cell, and 4 longitudinal nervures, the 2nd 

 and 3rd united towards the base, the 3rd and 4th towards the 

 margin ; balancers small, clavate : 6 legs tapering ; feet long, 

 slender, and 5-jointed, terminated by minute claws (fig. 59 ; z, 

 the natural dimensions). 



The larvae are 2^ lines long, of a whitish colour, tapering to- 

 wards the head, composed of 12 joints; on each side of the tho- 

 racic segment is a short branching spiracle, and the tail is fur- 

 nished with 4 divaricating blunt spines, the edges of the segments 

 being serrated with hooked ones (fig. 60; a, the natural size). 

 When full grown, this skin becomes horny, changing to a rust- 

 colour, the maggot is transformed to a pupa within an internal 

 horny shell of a chestnut colour, and of course the pupa (fig. 61 ; 

 b, the natural size) greatly resembles the larva. 



There is also an extensive group of flies called Borborus* the 

 larvae of which live upon decomposing vegetable, and probably 

 animal substances also : at all events they are generated in fungi. 

 A portion of these flies is now distinguished by Macquart under 

 the generic name of Ltmosina ;t one of them 1 have bred from 

 rotting potatoes, and it seems to be identical with that author's 



37. L. geniculata.J It is only 1 line long, and expands a little 

 more than 2 lines. Tt is black ; the head is moderately large, 

 with an ample cavity beneath to receive the mouth : the eyes are 

 hemispheric and rust-coloured, and there are 3 minute ocelli on 

 the crown ; the face Is concave, with 2 little horns in the centre, 

 the 3rd joint orbicular, with a tomentose seta: thorax broader, 

 very convex ; scutel semi-orbicular and flat : abdomen very short, 

 the segments equal in length : wings rather small, smoky, nervures 

 pitchy ; costal the strongest ; subm^arginal cell not extending to 

 the apex, 2nd and 3rd longitudinal nervures united at the middle, 

 3rd and 4th forming a loop with 2 minute branches at the ex- 

 tremity ; balancers small and ochreous : legs pitchy; hips ochre- 

 ous, as well as the tips of the anterior thighs and the base of the 

 shanks; hinder with a few spines outside; feet long, 5-jointed, 

 especially the hinder, which are slender, and longer than the 

 shanks ; dull ochreous, basal joint very long and pitchy, terminal 

 one very short, and furnished with short claws, 



M. Rayer also observed a species in the infected potatoes which 



* Curtis's Brit. Ent., fol and pi. 469. 



f Curtis's Guide, Genus 1350. 



i Macquart's Hist. Nat. des Dipteres, vol. ii. p. 572: 



