There are two, possibly unconnected, Castaigne families mentioned in The Carcosa Mythos. The first is that of cousins Hildred and Louis Castaigne (to which might be added Henri de Calvados Castaigne). The second is that of Mrs Castaigne and her daughter Constance Castaigne. Other references to Castaignes may or may not be connected to one or both of these families. A third family, bearing the modified name of del Castaigne, also exists in the fiction. See also Xastain01.