http://upload.wikimedia.org/wikipedia/en/f/f0/Bobcat_sitting.jpg


http://www.socogardenszoo.com/Bobcat%20-%20Bobbie.jpg

---even in this pic with similar coloration to a mountain lion you can notice the difference in the texture of the coat ---

http://www.sawtoothadventures.com/MountainLion.html
---this site has both pics of a really big bobcat and a couple of mt lions - you can see the size of the tail on all the mt lion pics and on one of the pics you can see that the mt lion does have a very light/white underbelly and white under the chin and on the neck - Also notice the texture of the coat compared to the bobcat pics - the mt lions coat is much more corse.