>It was identical to the one on the left.
>http://upload.wikimedia.org/wikipedia/en/d/d5/Horned_lizards.jpg

Ok, it was a rountail ( P. modestum ) then. The one on the right is a DHL ( P. platyrhinos ).

>My girlfriend's sister bought this lizard on an impulse buy not >knowing anything about lizards she left it with me. Let this be >a lesson to all. If you don't know about an animal don't bring >it home.

Amen to that. I'm sorry to hear about it. This is sadly the disposition for 90 % of Horned Lizards captured and/or sold willy nilly to the general public. It's sad that these human impulses to keep something "cute" usually end up killing the animal.
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"A man that should call everything by it's right name, would hardly pass the streets without being knocked down as a common enemy." The Complete Works of George Savile, First Marquess of Halifax 1912,246