A type of gallery grave having side chambers resembling transepts; a variant of the megalithic gallery grave in which side chambers (transepts) open from the main burial chamber. These tombs are found only in three areas: near the mouth of the River Loire in France, in the Bristol Channel region (e.g. Severn-Cotswold), and in northwest Ireland. The three are in some way interrelated and all lie on western seaways linking Atlantic France with the British Isles. Some scholars regard those in France as variant passage graves, unrelated to the British Isles tombs.