Kamasutra 2.6.22

2.6.22

tadāndhrīṣu prāyeṇa/ iti saṃveśanaprakārā bābhravīyāḥ//

When the woman forcibly holds in her yoni the lingam after it is in, it is called the "mare's position." This is learnt by practice only, and is chiefly found among the women of the Andra country.

The above are the different ways of lying down, mentioned by Babhravya; Suvarnanabha, however, gives the following in addition.