Wicked mesh deform: Misusing bones, meshes or both? I have a sea turtle mesh and skins I have created in ZBrush and Blender, and I spent some time in Blender trying to make as nice a mesh as I know how... or at least as I think I know how. 

For the head, neck and much of the rest of the critter I get good movement and deformation of the meshes and skins, except in the armpit... when the flippers meet the body. See the images I have attached.

 

Although that showing the tearing at maximum bone movement, it shows up with almost any movement.

Am I asking individual bones to do too much? Add more bones and reweight? Or should I have built more crenellation into the skin, so there are true folds that can move? And/or have a I missed something even more obvious? The tearing and stretching of the mesh is more than I have seen in other rigs we've done, and leads me to think I am missing something really fundamental about geometry and weightpainting...

Thanks!
Actually... I threw away everything and recreated, using face masking to assure good delineation of weights.... but that leaves two variables to explain it: better bone alignment to the intended motion of the critter, and more precise weight painting. Face masking rocks.  This is the final one... I did not get a weight view of the faulty one.