Note 25 — 1. Family BALANIDÆ, (or Sessile Cirripedes).

In the case of Coronula there is a peculiarity, described in the last section of this Introduction, (under the head of Cementing Apparatus), namely, that the two or three last-formed, exterior zones of the Basal membrane continue for a period to increase in width; being, as I believe, dragged one from over the other, with fresh laminæ of membrane continually thrown down. In this same genus, and in Tubicinella, the walls of the shell are invested by membrane, which is doubled inwards under their basal edges; and as the latter grow, the investing parietal membrane splits and separates from the basal membrane, and is pulled outwards and downwards. This inflected, often broad border of membrane, seems to me more strictly comparable with the opercular membrane, than with those narrow, thickened rims of yellowish membrane which in other Cirripedes cover the suture between the basal edges of the walls and the basis.