ABSTRACT
Creusia differs from Pyrgoma only in the shell being separated by sutures, into four compartments, with well developed radii: in other respects, such as in general habit, in the cup-formed embedded basis, in the opercular valves, in the characters derived from the mouth and cirri, there are no generic differences. The shell differs very little in the several varieties of species of Creusia; and the most marked difference, namely, whether the walls are permeated by irregular pores or not, seems certainly quite / variable. The shell is oval, generally flat, sometimes conical, with narrow and approximate ridges radiating from the orifice. The tergum, is the remarkable feature, being sometimes excessively narrow, with a long sharp spur, which often, but not always, terminates in a needle-like point. All these characters are variable in the several foregoing varieties, and they have been found, as yet, insufficient to discriminate species in any genus of sessile cirripedes.
