Note 104 — 2. Sub-Genus—ACASTA. Pl. 9.

In Mr. Cuming’s collection there is a specimen, from Sydney, which I fully believe to be the present species, but cannot be positively sure, as the opercular valves have been lost, which is very remarkable from the walls of the carino-lateral compartments being reduced to the thickness of a mere thread, not one twentieth of the width of the lateral compartments; we here see the structure of Acasta sporillus prefigured.