Wikipedia
Ditrysia
The Ditrysia are a natural group or clade of insects in the Lepidopteran order containing both butterflies and moths. They are so named because the female has two distinct sexual openings: one for mating, and the other for laying eggs (in contrast to the Monotrysia).
About 98% of described species of Lepidoptera belong to Ditrysia. The group can be divided into the primitive but paraphyletic "micromoths" and the derived monophyletic Apoditrysia, which include mostly larger moths, as well as the butterflies. Those with a dorsal heart vessel belong in section Cossina. Others, having a ventral heart vessel, belong in section Tineina.