The affix ka comes after root khyā 'to tell', when preceded by the preposition sam and when the object is in compsition with it.,
The verb ख्या ends in long आ and by 3.2.3 when compounded with an upasarga, it would have taken the affix अण्. This debars अण्; as गोसङ्ख्या 6.4.64 'a cowherd' (गा सञ्चष्टे).,