ABSTRACT

The subgenus is a very natural one, inasmuch as all the species are closely allied in essential structure, in general appearance. On the other hand, in the structure of the shell, in all the characters derived from the opercular valves and animal's body, Acasta cannot properly be distinguished generically from some species of Balanus. These differ in no generic respect from those of Balanus. The scuta are striated longitudinally in several of the species: the adductor ridge is barely developed in any, being most prominent in Acasta cyathus. The parts of the mouth are identical in the several species, and present no generic differences from / those in Balanus. In the animal's body the only noticeable character was, that on the anterior ramus of the fourth pair of cirri, some of the segments were furnished with very broad and thick, small, downwardly curved, teeth or hooks, like those described in certain varieties of Acasta sulcata.