What is "concavely"

Usage examples of "concavely".

The channels, though concavely curved, were smooth, and the dirt in them was no harder than wood.

What remained of it in my mind were the initial letter and the closing figure as if the whole amphitheater of six signs receded concavely behind a tinted glass too opaque to allow the central series to be deciphered, but just translucent enough to make out its extreme edgesa capital P and a 6.