iShell = Table[SphericalShell[{0, 0, 0}, {(i - 1) 0.1, i 0.1}], {i, 50}];
regInt = Table[RegionIntersection[iShell[[i]],
Cuboid[{-1, -4, -1}, {1, 4, 1}]], {i, Length[iShell]}];

Table[Region[regInt[[i]]], {i, 27, 29}]

intDisc = Table[BoundaryDiscretizeRegion[regInt[[i]],MaxCellMeasure -> .01], {i, 27, 29}]

pic = Table[Graphics3D[{intDisc[[i]], Opacity[0.5], iShell[[i + 26]],
Cuboid[{-1, -4, -1}, {1, 4, 1}]}, Boxed -> False], {i, 2}]