Hydrophis nigrocinctus
Range
Bay of Bengal: Sundarbans; also recorded from the Indian Ocean and Malay Archipelago
The black-banded sea snake is a venomous sea snake known from only three specimens. The first was described in 1803 and collected in the Bay of Bengal in the Sundarbans near Kolkata, the second was caught in the Malay Archipelago in 1896, and the third was found in February 2015 in the Sundarbans of Bangladesh, on the island of Dublar Char, and described in 2024 (Wikipedia, general species account).
The Reptile Database lists the Indian Ocean and Bay of Bengal. Given how few specimens exist, little else is known about it.