ABSTRACT
Xenobalanus may be described as a Tubicinella without opercular valves with the opercular membrane thickened down to the basisand with the shell, excepting the few last-formed basal zones of growth, almost wholly removed by the breakage of its upper end. In Xenobalanus similar ledges are less perfectly joined, and apertures seem always to be left in transverse rows under the transverse toothed ridges. The apertures, of course, are covered by membrane. The transverse ridges are surmounted by knobs arising from the longitudinal septa; and the knobs themselves are capped by other little heads. Xenobalanus is further allied to Platylepas, in the lesser size of the inner fold of each branchia, compared with the outer, and in the structure of the cement-glands, and to a certain extent in that of the sheath. Each branchia is double, the two folds being united where attached in a transverse line across the sack, on a level with the attachment of the body.
