Today I made this.
I am posting how I did it, not because I want to Help Humanity in it’s Quest for Sketchup Knowledge, (ketchup knowledge?) but because I know in about a week I’m going to forget how I did it.
So. Start with a circle. Draw a line with the pencil tool on one of the axis.
Then with the arc tool, peg the top and bottom of the line, and pull an arc out.
Use the Select tool to select the bottom circle.
Now, with the Follow Me tool selected, click on the arc section. You get this:
Mess around with the Push-Pull tool, and Bob’s your uncle.