What is the correct way to apply Sass conditionals inside a mixin?

I'm trying to exercise my Sass Basics by going back and doing CSS Foundations again, but refactoring everything to be in Sass. Obviously, this is overkill from an efficiency standpoint, but I figure it's good practice. Case in point, it's abundantly clear that I don't really know what I'm doing.

In this early lesson, Guil is showing us how to keep our code dry by combining selectors and creating three CSS shapes, a square, circle, and ellipse. To test myself I made a mixin instead and tried to apply some conditionals for the round shapes. It didn't work. Everyone's getting a border radius, even after I checked the syntax on the Sass documentation.

Obviously I'm doing something wrong. Any Sasstronauts available to tell me where I'm fudging this?

Code:

body {
    padding-top: 50px;
    text-align: center;
}

/* Shapes */

@mixin shape-base($shapes...) {
    @each $shape in $shapes {
        .#{$shape} {
            display: inline-block;
            margin: 0 15px;
            width: 200px;
            height: 200px;
            background-color: lightcoral;
            @if $shape == circle or ellipse {
                border-radius: 50%;
            }
            @if $shape == ellipse{
                height: 120px;
            }
        } 
    }   
}
@include shape-base(square, circle, ellipse);