258 MAINE AGRICULTURAL EXPERIMENT STATION. 1916. 



9. All of the segmental elevations and segmental spines, on the dorsal 

 surface of the body, of nearly equal size. The inter-spiracular 

 spaces on the stigmal plates with lamellate, upright ridges. 



(Fig- 35-^ and 5) Didea fasciafa fuscipes, p. 246. 



The dorsal, segmental elevations (ones next the median pair) in 

 the principal body-segments much reduced in size. The dor- 

 sal spiracular nodule long and prominent; the other inter- 

 spiracular spaces with small nodules or delicate hairs 10 



10. Posterior respiratory appendage broader than long 



Paragus tricolor (31, p. 397). 



Posterior respiratory appendage considerably longer than broad. 

 Paragus tibialis (31, p. 402) . 



11. Integumental spines black. Inter-spiracular spaces with short, 



stout, black spurs. (Fig. 32-46, 49 and 50) 



Syrphus americanus, p. 236. 



Integumental spines light yellow. Inter-spiracular spaces with long 

 slender hairs. (Fig. 29-^) Pipiza pisticoides, p. 224. 



III. THE SHORT-TAILED FILTH-INHABITING TYPE 



Key to Species 



i. False-head of larva without any conspicuous, black, anterior 

 thorns or chitinized hooklets. Posterior respiratory appendage 

 about three times as long as broad. The spiracles on stigmal 



plates with about ten lateral denticles. (Fig. 37-5 and 9) 



Syritta pipiens, p. 253. 



Antero-dorsal part of false-head ornamented with black hooks or 

 thorns, visible to the naked eye. Posterior respiratory appen- 

 dage less than twice as long as broad. The posterior spiracles 



with more than fifteen lateral denticles 2 



2. Two prominent hooks on each side of the false-head, their bases 

 united into one chitinous plate. The posterior spiracles with 

 forty to eighty lateral denticles Zelima (Xylota) pigra. 



Two prominent hooks on each side of the false-head, their bases 

 separated by a little more than their length; also several trans- 

 verse rows of slightly smaller thorns between these pairs. The 

 posterior spiracles with fifteen to thirty lateral denticles. (Fig. 

 36-5, 6, 7 and 8 % . Tropidia quadrata, p. 248. 



GLOSSARY OF NEW OR UNUSUAL TERMS. 



Anterior larval spiracle: The breathing pore, or opening to the 

 trachea, situated at the side of the third body segment of the larva 

 (Figs. 34-^; 32-466; and 36-5^). 



Anterior stigmata: See anterior larval spiracle or pupal respiratory 

 cornua. 



