Sacred rituals which are especially important in the veneration of ancestors are called?

Besides performing the function of achieving continuous group solidarity, the Behdienkhlam festival with its ritual and mythical expression also aim at achieving communal welfare and prosperity. A significant aspect of Behdienkhlam festival is the linkage between myth and ritual with preponderance of veneration of ancestress and Earth Mother by prayer, libation of wine and sacrifices. In the myth of U Lakriah and the ritual events we note a few important points: conception of a supreme God whose commandments from basis of religion ( Niam), who can be approached through the Mother Earth by prayer, Libation and sacrifice and the bones of the dead are to be preserved which has a correspondence with the megalithic myth of sookpoh and the ritual events such as lifting of logs representing three ancestress, and taking the sacred tree-trunk Khnong to go the sacred pool Aitnar, signify the veneration of the ancestors. The festival is celebrated after the sowing of seeds and rites are performed with chanting of myths ensuring good harvest. The ritual is decisively directed towards the veneration of the ancestress and is used for warding off plague and pestilence in order to ensure good harvest. The chanting of the myths of sookpoh and U Lakriah veneration of the four corners of Jowai of four stone deities as protectors of life and agricultural produce with sacrifice, cleaning of clan-cemeteries where bones of the dead are kept along with the use of tree-trunks and branches for warding off evil spirits are indicative of agricultural rites and ancestors veneration. This is usual with farming communities whose rituals are based on vegatation and fertility principles and ancestor cult.

Source: http://megartsculture.gov.in/herit_volII.htm