SYRPHIDAE OF MAINE. 211 



Rudimentary prolegs present. Anterior pupal respiratory 

 cornua elongate, cylindrical, very prominent. 



This type is most closely allied to the third type but differs from 

 it and from all the others in the remarkable elongation of the pos- 

 terior respiratory organ, which, in these species, is tube-like, three- 

 jointed and telescopic; and may be extended to several times the 

 length of the body although commonly contracted to about body- 

 length. This remarkable and highly specialized organ enables the larva 

 to carry on aerial respiration while feeding at various depths beneath 

 the water level. It is of two tubes fused mesad and enclosing two 

 trachese which open at the tip. The inter-spiracular ornaments con- 

 sist each of a single, unbranched, but plumose, long hair instead of a 

 palmate group of short plumose hairs as in the two previous types. 

 The prolegs are similar to type III. The anterior larval spiracles are 

 unusually conspicuous, borne on a pair of cornua which are capable 

 of considerable elevation although usually rather closely retracted. 



The shape of the body is sub-cylindrical with the anterior segments 

 forming a false head, and the mouth-hood as in type III. The terminal 

 segment tapers strongly into the respiratory process. The integument 

 is very flexible and transparent; segmental hairs double, similar- to 

 type III. The anterior pupal cornua are longer . than in type III and 

 nearly cylindrical, the enlarged distal part much longer than the basal 

 stalk, hence the whole less mushroom-shaped. 



V. THE MICRODON TYPE OF LARVA. 



Body hemispherical ; the flat surface ventrad, with a row of 

 spines around its margin; dorsum reticulated. Posterior respi- 

 ratory process short, the three spiracles on each half together 

 making nine lo.ops., convex outwardly and denticulated on their 

 outer margin. Inter-spiracular ornamentation of non-plumose 

 fine hairs. Mouthparts consisting of a ventral A-shaped jazv 

 and two dorsal pieces placed A-shaped, but not fused at the 

 apex. Segmental hairs and prolegs wanting. Anterior larval 

 spiracles apparently wanting. Pupal respiratory cornua morel- 

 shaped. : 



The larvae of this genus are very aberrant and superficially show 

 no relationship with the other larvae of Syrphidae, differing strikingly 

 from all the others in shape. Instead of the elongate, sub-cylindrical 

 body we have a nearly hemi-spherical body. The outline is short 

 elliptical, the ventrum very much flattened forming a ventral sole 

 around the margin of which is a circlet of ornamental spines. Dorsum 

 almost uniformly rounded up. Mouthparts open in a longitudinal slit 

 on the cephalic part of the ventral sole. Posterior respiratory process 

 dorso-caudad, short, tubular, but with some indication of its double 

 nature; circular plate medio-dorsad. The spiracular slits each of three, 



