Sowerby, G. B. II. (1868). Monograph of the genus Bulla. In: Conchologia Iconica, or, illustrations of the shells of molluscous animals. vol. 16, pl. 1-6 and unpaginated text. L. Reeve & Co., London. [stated dates: pl. 1, 5-6, March 1868; pl. 2-4, January 1868].