The affix ḍhañ comes in the sense of a descendant after the bases denoting quadrupeds.,
This debars अण् &c. Thus कमण्डलु + ढञ् = कामण्डलेयः 4.4.147, the उ being elided before ढ)). So also शौतिबोहयेः and जाम्बयः from शितिबाहु and जम्बु ॥,
चतुष्पाद्भ्यो ढञ्
Adhyāya 4 · Pāda 1 · Rule 135