230 MAINE: AGRICULTURAL EXPERIMENT STATION. 1916. 



Superficially the larva resembles most closely those of 

 Sphaerophoria cylindrica or Allograpta obliqua (q. v.) being 

 about the same size and similar in color and structure. How- 

 ever, besides the greater transparency of the integument in 

 this species, Melanostoma mellinum can be very certainly sepa- 

 rated from the other two species; first, by the shorter, more 

 nearly sessile, posterior respiratory organ which is less than 

 half as long as broad, whereas in Spikaerophoria cylindrica and 

 Allograpta .obliqua it is considerably longer than broad; sec- 

 ondly, by the greater length of the individual spiracles on the 

 posterior respiratory process in S. cylindrica and A. obliqua. 

 In M. mellinum the slit-like spiracles are less than twice as 

 long as broad, while in the other two species they are each at 

 least three times as long as broad. 



Puparium. (Fig. 30-7, 8, p). Length 6 'to 7 mm., width about 2 mm. 

 to 2.25 mm., height about 1.7 mm. to 2 mm. Usually broadest and 

 highest about the anterior fourth. Very moderately elevated, the pos- 

 terior half of the body being especially attenuated, the dorsal line 

 descending very gradually to the posterior respiratory process. Color 

 dilutely greenish or yellowish. The larval skin retains its great trans- 

 parency in the puparium so that the developing imago is quite plainly 

 discernible. On this account this is one of the very few puparia of the 

 aphidophagous type on which anterior pupal spiracles or cornua can 

 be detected. These (Fig. 30-7 A) are located near the cephalo-dorsal 

 corner of the puparium and appear as mere specks even at moderate 

 magnification, being about .025 mm. across. Hence they would be entirely 

 obscure (as they are in most related species) if it were not that the 

 relatively large trachea! trunks leading from them to the prothorax of 

 the nymph can be discerned through the puparium. 



When highly magnified (Fig. 3O-&, o) the pupal respiratory cornuum 

 is seen to be a nearly cylindrical elevation, a half longer than broad 

 and the end differentiated into eight denticles, evenly distributed and not 

 contiguous, around the circumference of the apex and extending a short 

 distance down the sides. Each denticle oval in outline, several times as 

 long as broad. 



Adult. (Fig. 30-70, n, 12, 73). Length 6 to 7 mm. A brilliantly 

 shining, metallic black species with bright yellow spots on the abdomen; 

 facial tubercle small; hind metatarsi not thickened 



In the male the frontal triangle a little prominent with a pit in the 

 middle; in the female the frons with a broad shallow transverse de- 

 pression. Frons and face shining, whitish-dusted' on the sides. Antennae 

 yellow to black, usually brownish on upper half, yellowish below except 

 at tip of third segment, arista very briefly and short pubescent, nearly 

 bare, yellow at the base. Abdomen in the male (Fig. 30-75) about four 

 times as long as broad, dull black with three pairs of yellow spots; the 



