Key to Thai species of Ptilocerembia (adult females)

1. Head and prothorax unicolorous........................................................................... 2

- Head clearly darker than prothorax......................................................................... 3

2. Head and thorax blackish; abdomen mostly dark with white stripe on lateral plate, basal three abdominal terga blackish in contrast with the next four brown terga; terminal three abdominal segments dark brown; coxae and trochanters whitish, strongly contrasted by the dark femora tibia and tarsi............................................. P. thaidina sp. n

- Head and thorax dark. Abdomen with white stripe lateral on plate and conspicuous pale longitudinal mark on a dark background; tibia and tarsi darker than other part of legs........................................... P. catherinae sp. n

3 Head light brown; prothorax yellowish; meso- and metathorax brown to dark; legs largely yellow; abdominal terga 1–3 dark, terga 4–7 yellowish, and terga 8–10 dark brown................................................... P. rossi sp. n.

- Head brown to dark; prothorax yellowish with two longitudinal brown bars; coxae and trochanters yellowish; femora and tibia, except for short basal and terminal yellow area, as darkly colored as tarsi; abdominal terga 1 and 2 dark, tergum 3 with wide pale colored patch on a dark background, terga 4–6 yellowish, terga 7–10 dark brown............ P. senathami sp. n.