Neohydrocoptus jaechi(Wewalka) is recorded for the first time in Egypt. It is very similar toN. angolensis(Peschet), but there are aedeagal differences. The karyotype consists of 6 pairs of autosomes and sex chromosomes which are neo-XY (♂) and neo-XX (♀). C-banding shows that the sex chromosomes ofCanthydrus diophthalmus(Reiche & Saulcy) are not the small pair suggested by Bilton (1992), but are one of the largest pairs, with the Y-chromosome totally heterochromatic. The implications of these findings are considered in the light of Belkaceme's (1991) work on the phylogeny of Noteridae.Neohydrocoptusis placed among the group of more primitive genera, outside the closely-knit group of higher Noteridae, whileCanthydrusis placed right at the top of the higher Noteridae. The neo-XY sex chromosomes ofNeohydrocoptuscould be a primitive condition for the family, while the system found inCanthydrusis derivable from that ofSynchortusSharp (Saleh Ahmed et al., 1997) (one of Belkaceme's basal genera of the higher Noteridae) by loss of the mainly heterochromatic X2-chromosome, leaving the more normal X1-chromosome and the Y, which is almost entirely heterochromatic inSynchortusand completely so inCanthydrus.