In Tantra, the various Mantras from the five, six or ten āmnāyas are considered to originate from the different faces of Paramashiva.
In general, the six faces of Paramashiva and the corresponding āmnāyas that originate from those faces are:
1. Tatpuruṣa- Pūrvāmnāya
2. Aghora – Dakṣiṇāmnāya
3. Sadyojāta- Paścimāmnāya
4. Vāmadeva- Uttarāmnāya
5. Iṣāna- ūrdhvāmnāya
6. Svacchanda- Anuttarāmnāya
However, in the case of Srīkula Tantra, the six āmnāyas originate from the following six faces of the Lord, who receives the sacred knowledge of these recessions from Mahātripurasundarī Herself:
Ananda Bhairava, Dakṣiṇāmūrti, Virūpākṣa, Rājarājeśvara, Sadāśiva and Saṃvarteśvara.
Even in the case of Mahāvidyā Kālī, the mantras originate from the same faces. However, the scheme is completely different in the specific case of Guhyakālī and Kāmakalā Kālī. While the eighteen lettered mantra of the latter follows the earlier scheme, the twenty-eight lettered mantra which attains tādātmya with Tripurasundarī follows the below discussed scheme specific to Guhyakālī. All these Mantras originate from the lotus faces of Bhagavatī Guhyakālī.
– The ūrdhvavaktra of the Great Goddess is called Dīpaka and from this face twenty Tantras originate. The deity of this āmnāya is Chaṇḍayogīśvarī.
– Below that is the lion face (siṃhavaktra) from which ten Tantras emanate. The deity of this face is Siddhakālikā.
– Below this face is the jackal face, which is dark in color and giving rise to thirteen Tantras. The deity of this face is Mahāsaṅkarṣaṇa.
– To the left is the monkey face called Kapīndra-vaktra, from which twenty-five Tantras originate. The deity of this face is Kubjikā.
– On the right is the boar face (sūkaravaktra), called Trailokyaḍāmara, and from this face originate eight Tantras.
– Further left is the face resembling the Garuḍa, represented by Sundarī, giving rise to sixty-four Tantras.
– On the right is the yellow-hued crocodile face from which sixty-four Tantras originate. The deity of this face is Mahāsaṃhāriṇī.
– To further left is the crystalline elephant face giving rise to nine Tantras. This face is represented by Pratyaṅgirā.
– On the right is the dark horse face (hayāsya), presided over by Siddhayogīśvarī. From this face, thirty-six Tantras originate.
– Finally, from the secretive faced named Siddhikarālī, sixty-four Tantras emanate.
Thus, eight faces of the Great Goddess represent the āmnāyas of the eight directions and the other two faces give rise to Tantras and Mantras of ūrdhva and Pātāla āmnāyas.