Assistance in identifying Roman coin

Hi, I'm completely new to ancient coins.  Would someone please help me identify the specifics of this coin?

What I know (from a certificate of authenticity with it) is that it's an Imperial Roman bronze coin, minted between the 1st and 3rd centuries A.D. during the Constantinian Empire.  I located this site, but I've not had much luck locating my specific coin:

http://www.forumancientcoins.com/catalog/roman-and-greek-coins.asp?vpar=440&pos=0#Constantinian-Era

Any assistance would be much appreciated.
Thank you.

 

please browse this site:
http://www.wildwinds.com/coins/ric/i.html#C

Цитата: PetrusAscanusplease browse this site:
http://www.wildwinds.com/coins/ric/i.html#C

Constantius Gallus (Caesar 351-354) Obv. / "Fallen Horseman" Rev.

Thanks!  That site sent me on my way.  I'm still trying to determine the mint location as much as possible, which is difficult with the condition of the coin.  I'll have to continue pattern matching the image until I find it.  Had no idea there where so many variations with these ancient coins, but now that I think about it I can understand why.  I appreciate your help.