This is a natural white conch shell (Tib. dung dkar; Skt. shankha), silver-plated and fitted with a metal mouthpiece.

"Vedic Brahmanism and later Buddhism adopted the conch as a symbol of religious sovereignty and an emblem which fearlessly proclaimed the truth of the dharma. …As a Tibetan ritual musical instrument the conch is ornamented with a metal mouthpiece, and an ornamental metal casing extending from the shell's mouth. This copper, bronze, silver or gold casing is embellished with auspicious symbols and designs."

— Robert Beer, The Encyclopedia of Tibetan Symbols and Motifs, p. 184

Details

• Length: 10 in (25.4 cm)
• Width: 4.25 in (10.8 cm)
• Height: 3 in (7.6 cm)
• Material: Natural conch shell, silver-plated
• Origin: Nepal