Congratulations, EGS, you have a very valuable coin. If it is genuine, it is worth thousands of US dollars. However, rare coins like this are often counterfeited and, if you have a fake, it is worth zero.
The obverse of the coins changes with the reigning British monarch. Coins dated 1835 feature a bust of King William IIII, while coins dated 1841 display the likeness of Queen Victoria.
The coin in our photo is a genuine William one mohur dated 1835 sold by Ira and Larry Goldberg of Beverly Hills, USA for the astounding sum of $12500 US dollars during a 2013 auction. A two mohur coin, which looks the same, sold for $19500 the same year. You get the idea that this is a valuable coin.
The 1841 issues with Victoria are not quite as scarce, but still very valuable, with coins selling for $3000 to $4500 when they are fully uncirculated.
CoinQuest, once again, thanks the Goldberg's for use of their amazing coin photographs. This one knocks your socks off.
If you think your coin might be genuine, you should take it to a knowledgeable collector or professional coin dealer for an in-person appraisal. He or she can probably tell authenticity by close inspection. You can find a listing of super-honest coin dealers on the PNG Dealers web site.
You can send pictures to CoinQuest and we can give you our opinion about your coin (use the Contact Us link to start an e-mail exchange), but, for coins like yours, an in-person appraisal is best.