Among the most aberrant types of pollen grains found in plants which have been referred to the family Acanthaceae, are those of the genera Meyenia N. ab E. and Thomandersia Baill. Although the pollen grains were described by LINDAU under different names, those of the first genus as cogwheel-shaped and those of the latter as lenticular, they are really very similar: in both genera they are depressed globose, provided with five or more meridional grooves extending from the equator to about halfway the poles, and without clearly circumscribed germ pores. The difference between the two kinds of grains lies in the presence or absence of ribs: in Meyenia the grooves are borne on the top of ribs separated from each other by shallow depressions, whereas in Thomandersia the whole surface between the grooves is more or less evenly bent. Material of Meyenia was not yet available to me, but judged from the description the genus differs but slightly from Thunbergia L.f. sensu Lindau. In fact, the two genera have often been united. The pollen grains of Thunbergia sensu Lindau resemble those of Meyenia in the absence of germ pores and in the presence of grooves, but the latter are never meridional: as a rule, they are more or less serpentine (cf. BREMEKAMP in Rec. d. trav. bot. néerl. XXXV, 1938, pp. 142—143, fig. 2 A—G and Tab. XIII B—E).