Many Polybothris seem to be pushed by natural selection to become very flattened and with a large and rounded body. This is got developping large and flattened expansions of prothorax and elitrae. Probably this is very good for mimicry when they stay on bark. They are also mostly coloured in dark colours (from black to dark brown, dark copper, dark green, etc.) on their dorsal surface, while they are with extremely bright colours underside. These colours are very probably important for sexual recognition. So we can find species very similar one to another in their dorsal view, but with very different colours underside.

Polybothris auriventris

This is one example of this differentiation: two species (Polybotris auriventris and Polybothris bernieri), very similar on the top (they are very difficult to identify without checking ventral side), are very different underside.

Polybothris bernieri

We can find a long series of species where rounded body shows a growing development. Here we can see some of them.
 
 

Polybothris pyropyga	Polybothris mucronata	Polybothris quadrispilota
Polybothris humboldti	Polybothris strigithorax	Polybothris emarginata
Polybothris carinifrons		Polybothris geminata
Polybothris coccinella	Polybothris auriventris	Polybothris sp.

The beautiful (one of the most colourful species, underside) and quite common species Polybothris quadricollis seems to be an intermediate form between this series and the other one, where just prothorax show lateral expansions

Polybothris quadricollis