That's Biel / Bienne, see its coat of arms:
By Aliman5040 - Own work, CC BY-SA 3.0, Link
Swiss historian Markus Kutter confirms it in Zwischen Jura, Vogesen und Schwarzwald, 32. Hinter die Fassade verbannt (in German):
Auf der ursprünglichen Fassade waren nur 11 Wappen abgebildet, also die achte alten Orte, ergänzt durch Freiburg und Solothurn, dazu Basel. Beim ersten Umbau des Rathauses von 1606 bis 1611 kamen Biel, Wallis, Graubünden, St. Gallen, Appenzell und Schaffhausen dazu.
Bienne's coat of arms was added between 1606 and 1611 (the article is about why Mulhouse is at the back).
More explanation, gleaned from Kutter:
The coats of arms consist of the Swiss cities (first 8, then 11) and its associates Biel, Wallis, Graubünden and St. Gallen. Here's an overview of the growth of the Old Swiss Confederacy. You can also see other associates, above mentioned Mulhouse and Rottweil.