Śaiśirīya Śikṣā 89

89

eṣa chedo vivṛttīnāṃ yathāmātravicakṣaṇaḥ
vatsānusṛtārdhamātrā tathā vatsānusāriṇī

this division of hiatuses is known according to mora: / the vatsānusṛtā has half a mora, and likewise the vatsānusāriṇī;