Bengali here is not one thing, and the split matters more than the label. The Bhagirathi belt speaks the Nadia end of the Rarhi group — the variety colloquial standard Bengali was standardised from in the nineteenth century, which is why a Santipur speaker sounds unaccented to a newsreader and a Faridpur speaker does not. East of the live channels the Bangali varieties take over, with different verb inflections, a different vowel set and a fricative where the west has an aspirated stop. Millions of speakers of eastern varieties have lived in the western delta since the mid-twentieth century, so both are now spoken in the same streets, and the Ghoti–Bangal distinction is a linguistic fact before it is a culinary joke.
Rarhi (Nadia–Kolkata)Indo-Aryan, Eastern
The Nadia–Santipur–Krishnanagar speech that the nineteenth-century prose reformers took as their model, and which Kolkata then made the prestige register of a whole literature.
बोलने वाले: The base of standard Bengali, spoken as a first variety across the western delta
Bangali (eastern delta)Indo-Aryan, Eastern
Dhaka, Faridpur, Barisal and Jessore varieties, now also spoken across the western delta. Differs from the standard in verb endings, in the treatment of aspirates, and in a large vocabulary of tide, boat and net.
Sylheti-influenced eastern fringeIndo-Aryan, Eastern
At the delta's north-eastern rim, where the plain meets the Barak and Surma country, the speech carries Sylheti phonology and its own script tradition in Sylheti Nagri.
Musalmani BengaliIndo-Aryan, Eastern
Not a separate dialect but a register with a heavy Perso-Arabic vocabulary — pani for water, gosol for a bath — used in the eastern and Murshidabad-side Muslim households and in the puthi literature printed for them.
Kokborok contact zoneSino-Tibetan, Bodo-Garo
On the delta's eastern hill margin the Bengali of the plain meets Kokborok. The plains Bengali there carries loanwords in the other direction, and bilingualism is the norm rather than the exception.