[<< wikipedia] V-shaped passage grave
V-shaped passage graves  are a type of megalithic chamber tomb found in parts of Atlantic Europe including Ireland and the Channel Islands. They date to between 3500 and 2500BC.
They are similar to Wedge-shaped gallery graves in that in plan they have a narrow entrance that widens out inside into a burial chamber. The entrance passage and the burial chamber are distinguished by sill stones however meaning that they are part of the passage grave tradition. 
In some cases a small sub chamber leads off from the main chamber.
Examples include La Varde and Le Creux es Faies on Guernsey.