The Henry Classification System

(Forensic Press, 2000)

Arches can be classified as a plain arch or as a tented arch. 
A plain arch is a pattern where the ridge enters one side and flows out
of the opposite side.  The ridges
rise or make a wave in the very center of the pattern. 
A plain arch does not have any recurves, angles, upthrust, or looping
ridges.  If any of these are
present in an arch pattern, then it is a tented arch pattern. 
Tented arches may have at least two (2) of the same characteristics of a
  loop.  A tented arch may have a
ridge count, recurve, or even a delta present in the pattern. 
Most tented arches have a looping ridge existing in the pattern, but this
does not hold true for all tented arches. 
An easy way to remember a tented arch, is that it looks similar to a tent
like formation. The Henry Classification code for tented arches in fingers 2 and
7 is a capital T.  In all fingers
other than 2 and 7, place a small t in the fingerprint block. If the print or
impression is classified as a plain arch, place a capital A in the box for
fingers 2 and 7, all other fingers that are not 2 or 7 will have a lower case a
to indicate a plain arch.      

(Forensic Press, 2000)