VECTOR

i got a quick an easy approach for this, i'll do a rough example and write up brb
 
EDIT - just noticed there appears to be another ring running horizontally ( i presume this is the view from underneath )  to add this you would just repeat the process already outlined below.
 
 
Okay so here's a quick approach. Not sure on the particular shape of these, so i presume its something along the lines of this.
 
1) grab a standard sphere, give it 12 segments and make it editable, remove the top centre faces, and adjust the topology of the sphere at the bottom with something like the example below to avoid a nasty pole, shading errors etc
 
2) Next put the sphere under a subdivision object set to one and make it editable. Add an edge loop either side of the centre line on X/Z as shown below.
 

 

 
3) Select the opening edge, as well as your centre lines on the mesh and do an edge to spline command ( you may wish to subdivide it further for a smoother curve ) put this to one side we'll use it later. Go back to your mesh, with your centre loops selected and scale them as shown below.
 

 
4) final stage is to sweep our spline and place it inside our mesh under a subdivision object and adjust accordingly.