What do you call a fish eye lens without the circle in the middle of the picture?

There are two kinds of fisheye lenses; circular and diagonal. The cheap fisheye lenses (including those lens adapters) are circular, while the more expensive and better fisheye lenses are diagonal. A diagonal fisheye is linear in the vertical and horizontal center planes, but "fisheye" in just the corners. Here is a photo from a circular fisheye lens: http://www.sigmaphoto.com/client/images/productphotos/08142009_img_97451.jpg And a photo from a diagonal fisheye lens: http://www.sigmaphoto.com/client/images/productphotos/rr-nike.jpg All wide angle lenses do exhibit some distortion, called "perspective distortion". This distortion becomes more pronounced as the angle becomes wider. A wide angle lens is designed to minimize this distortion, while a fisheye lens is designed to maximize it. In a true sense, a fisheye lens is a special effect lens.

It's still a fisheye lens. I'm guessing you are actually referring to a semi-fisheye adapter that screws-in to the front end of your existing lens. When attached to the 18-55mm kit lens, the semi-fisheye adapter will produce that circular image at the 18mm end and not at the 55mm end.