A new species of Dayongaspidae, Dayongaspis colubra sp. nov., is described from the Telychian (Llandovery, Silurian) Xiushan Formation at Maoyanhe Town, Zhangjiajie, Hunan Province, China. The new species is distinguished from the type species D. hunanensis by its larger-sized headshield, tiny and dense granular tubercles, and triangular-shaped inner cornual processes. Additionally, it reveals more galeaspid plesiomorphic characters than D. hunanensis, such as the inverted splayed posterior supraorbital canals (soc2) and the paired endolymphatic openings on the headshields. This new finding represents the first fossil record of galeaspids in the Xiushan Formation, thereby enriching the diversity of galeaspids. Furthermore, it extends the Wentang Vertebrate Assemblage upwards into the lower part of Xiushan Formation, indicating a broader stratigraphic range than previously assumed.