113a:
Head with subgenal ridges that fit against fore coxae when
head deflexed; prosternum in front of coxa narrow, shorter
than intercoxal process
Scirtidae p. 417
113
b:
Head without
subgenal ridges, genae usually not in contact with fore
coxae; prosternum in front of coxa nearly as long as or
longer than intercoxal process