There's only so specific I can get on a coin in this rough condition. The reverse depicts two soldiers around 1 standard, with "GLORIA EXERCITVS" (meaning "Glory of the Amry") surrounding, and a mintmark below. If I recall correctly, coins like this with one standard were introduced shortly before the death of Constantine in 337, and they lasted until 340 or so. Most likely, the coin depicts one of Constantine's sons, though I can't really make anything out on the obverse to tell you more than that. In terms of value, it's honestly pretty much worthless in this condition.
it looks kinda similar to my coin http://www.cointalk.com/t101290/#post853630 I believe it is this the 3rd or 4th one down here: http://www.anythinganywhere.com/commerce/coins/coinpics/rom-4ccon&.htm
As per Gao's response - Constantinian Dynasty, Gloria Exercitus type, mid 4th century AD. No further attribution is possible in this type.
