This is called a transition from 'dotaku to hear' to'dotaku to see' (Taku TANAKA), and many of the latter one have ears (round or half-round ornament) on the edge of the crown and the fin (decorative plate along the body side).
これは「聞く銅鐸」から「見る銅鐸」への展開と呼ばれ（田中琢）、鈕・鰭外部に耳が付くことが多くなる。