Extrabuccal infralabial secretion outlets in Dromophis, Mimophis and Psammophis species (Serpentes, Colubridae, Psammophiini). A probable substitute for 'self-rubbing' and cloacal scent gland functions, and a cue for a taxonomic account.

Extrabuccal infralabial secretion outlets (ILOs), periodically absent and heretofore non-described, have been found in nineteen species representing three of the eight psammophine snake genera. These infralabial outlets are thought to be non-existent in the other five genera. A few psammophines representing four genera, among which three of the five without ILOs, are characterised by their 'self-rubbing' behaviour, for which they employ an external narial valve bearing a secretion outlet of a special nasal gland. Such a valve is here reported for representatives of all eight genera. It is proposed that all psammophines perform self-rubbing to enable subsequent chemical marking of substrate and conspecific individuals. The newly found infralabial outlets, however, serve for direct chemical marking of conspecifics. This direct marking seems to substitute for a function of both the special nasal gland and the cloacal scent glands during social activity of the snakes in trees or shrubs. This hypothesis and the relationship of the observed traits with the presumed advantages of a thin and short hemipenis are discussed. A taxonomic implication is suggested.