ABSTRACT
This chapter discusses the relations of the Chthamalinae to the Balaninae, and of the several genera to each other. The shell in this subfamily consists of four, six, or eight compartments, with the addition, in Catophragmus, of several whorls of supplemental compartments or scales, like those forming the lower part of the capitulum in Pollicipes. The rostrum has alae and no radii; in shape and size it resembles the carina. The rostro-lateral compartments are destitute of alae; in all cases they overlap the adjoining compartments, and have radii on both sides. In the genus, Pachylasma, however, the shell must be looked to very young, in order to detect this normal structure, for soon the true rostrum and rostro-lateral compartments become blended together, making a compound rostrum, destitute, as in the Balaninae, of alae, but furnished with radii. The scuta and terga are articulated together more deeply than is usual in the Balaninae; and the terga never have a long spur.
