This is a captive female Cx. quinquefasciatus ovipositing as part of a study on fecundity I am doing. The egg raft is forming between the hind tarsi. This genus oviposits in rafts, which float on the water's surface until hatching (typically takes 30 or so hours).
The eggs will darken before hatching, so the raft will look dark.
Note: wild examples of this species are much prettier. Too much inbreeding and lack of selection has reduced these guys to looking pretty ugly.