What is the object on the front of Larson and Edwards' calculus and pre-calculus textbooks called?

Question

There is this incredible glass figure on the front of my Calculus textbook, I searched online for what this figure is called and the formula for creating it, but I can't find it. I think it is a variation of the Klein Bottle.

Here is the image:

Answer 1

It looks like an umbilic torus:

http://upload.wikimedia.org/wikipedia/commons/1/12/Umbilic_Torus.png

^{From Wikipedia.}

Zev Chonoles pointed out another cover with the equation for the umbilic torus:

Answer 2

It seems to me to be a thickened (and rather heavily stylized) Möbius strip, i.e., a torus with square cross section that is given a one-half twist.

I made this image just now using the code from my math.SE question, Drawing a thickened Möbius strip in Mathematica