Caenis Demoulini, a new Ephemeropteron from Thailand

During a short stay at Bangkok on December 3rd, 1953, Professor H. Boschma observed that enormous quantities of minute insects were attracted by lamplight in the hotel of the Royal Dutch Airlines (K.L.M.) "Plaswijk" at the airport Laksi. From the enormous accumulations of these insects around the lamps he collected a sample which he entrusted to me for examination. This sample proved to consist almost entirely of a new species of mayfly which is described in the present paper. Caenis demoulini nov. spec. Female imago. Head and thorax uniformly yellowish brown. Eyes purple-black, prominent. Antennae grey-brown ; median ocellus prominent, colour light brown with a darker edge. Abdomen pale yellowish brown, at the dorsal surface with light browngrey markings, except on the last three tergites. Ventral surface paler, especially the last three segments. Stigmata in or near a faint black or grey spot. Cerci and filum terminale silver-white, rather densely covered with stiff, long, silvery hairs, except at the base of these caudal filaments, where the colour passes into a very light brown, whilst here the hairs abruptly become much shorter, and are placed more densely. Anterior legs grey-brown, median and posterior legs pure white with a very faint yellowish spot at the end of the femora. Wings vitreous, veins light grey, except subcosta and radius, which are dark grey-brown. Area subcostalis very light ferruginous. Measurements: body Q 3.5 mm wing Ç 2.9-3.0 mm