SuBFAMILY CALLIPHORINAE 951 
Length. 5.0-8.5 mm. 
Distribution. Nearctic: Southern United States. 
Biology, immature stages, and habits. Egg. The eggs are de- 
posited in batches of approximately 100 on carcasses, especially 
in or near crevices about the natural openings. 
Melvin (1934) found that eggs of pallescens failed to hatch at 
temperatures below 74° or above 104° F. At the lower limit 
15.06 hours were required to complete incubation and at the 
upper limit 8.91 hours. He also found the optimum tempera- 
ture to be apparently about 99° F., at which development was 
completed in 7.72 hours. 
Larva. First instar: Spines almost without pigment, their 
distribution difficult to determine; segments 2-7 each with com- 
plete band of spines at anterior border; posterior border of seg- 
ment 11 with two to three dorsal rows of heavily pigmented 
spines, but these apparently absent on dorsal surface of each of 
segments anterior to segment 11. Tubercles on segment 12 
small; in same relative position as in later instars. Cephalo- 
skeleton (pl. 41, A) very small and weakly developed; labial 
seclerites not prominent and hatching spine short; pharyngeal 
sclerites narrow, ventral cornua narrow and tapering to sharp 
point; anterodorsal projection of pharyngeal sclerites long, ap- 
proximately two-thirds as long as dorsal cornua. 
Second instar: Spines small and colorless to light brown; 
segments 2-7 each with a complete anterior band of spines; seg- 
ment 8 with spines usually absent or very small and lghtly 
pigmented on dorsal surface; posterior border of segment 11 
with several dorsal rows of spines; segment 10 without dorsal 
spines. Tubercles on border of -stigmal field small, relative posi- 
tion as in third instar. Cephaloskeleton (pl. 41, B) distinct and 
easily distinguished from those of other species, the most striking 
difference being in the appearance of the labial sclerites; entire 
leneth from tip. of labial sclerites to tip of dorsal cornua 500-550 
microns (in other species this length is at least 600 microns and 
sometimes it is greater than 700 microns). Anterior spiracles 
with four to six widely separated branches, more often with five. 
Third instar: Spines not prominent, lightly pigmented; seg- 
ments 2-8 each completely encircled with spines at anterior bor- 
der; segment 9 generally with one or two irregular and broken 
dorsal rows, but these may be absent for a short space; spines 
restricted to ventral and lateral surfaces on segment 10; segment 
11 posteriorly with three to four dorsal rows of spines; segment 
10 without dorsal spines; distribution of spines as in sericata 
