SYRPHIDAE OF MAINE. 251 



barely visible to the naked eye. The most posterior of these rows 

 (Fig. 36-7/4) consists of a large thorn at each side and six to ten smaller 

 ones between them. In the middle row near each side, and looking 

 much like a thorn, is located the sessile, anterior larval spiracle (Fig. 

 36-7.5). There is a small hook or thorn laterad of each spiracle, a 

 large one mesad and, between the latter, about three smaller ones. The 

 anterior row consists of six to ten thorns of moderate size. Cephalad 

 of these three rows and above the mouth-hood is a semi-circular band! 

 of numerous microscopic booklets. The surface of the anterior larval 

 spiracle bears four rounded nodules. 



The entire surface of the body is covered with microscopic, close-set, 

 pale brown, short, soft hairs. The segmental hairs are longer flexible 

 and about three in a clump. Eight transverse rows oi them can be 

 made out posterior to the anterior spiracles. The body segments are 

 further indicated each by a group of about four transverse wrinkles. 

 About seven pairs of prolegs, consisting of ventral fleshy projection's, 

 each bearing a clump of recurved booklets; five pairs on segments 

 five to nine, inclusive, about equally developed and with a dozen or 

 more booklets, the anterior ones largest; one pair on the venter of the 

 third segment which usually has fewer booklets, and a smaller pair 

 on segment ten. The anus is a prominent transverse slit about 2 mm. 

 cephalad from the base of the posterior respiratory organ, on the 

 venter of the eleventh segment. 



Color dirty white or clay yellow. 



Under laboratory conditions the larval period extended over 

 about two months from July to September. Although the larva 

 has been found only in human excrement, there is no reason to 

 believe it would not develop in other kinds of filth or decaying 

 material.* The larvae were found in the moist, but not watery, 

 portions of the mass and several inches beneath the surface. 



Puparium (Fig. 36-6", p, /o). Pale brown. Length 8 to 9 mm; maxi- 

 mum width 3.25 to 3.75 mm.; maximum height 2.75 to 3.25 mm. 

 Broadest a little in front of the middle where it is nearly circular in 

 cross-section. Only a little narrowed and globose in front, but evenly 

 tapering caudad to about one-third the width just in front oi the pos- 

 terior respiratory process. As viewed from the side, ventral line nearly 

 straight to within about two millimeters orf the posterior end, thence 

 elevated ; the dorsal line a little more strongly and abruptly elevated 

 anteriorly than posteriorly. 



*Since writing this, I have found the larvae and puparia at Presque 

 Isle and Houlton, July 8 and 9, in masses of rotting potatoes which had 

 beep swept out of store-houses and allowed to lie on the ground until 

 well-decayed. Adults emerged from the puparia, July 19 and 20. 



Many adults were noted hovering apparently for the purpose of ovi- 

 posting about the above masses and also about decaying masses of 

 "sprouts" from potatoes used in planting. 



