ABSTRACT
The Thoracica may be divided into three very natural families, of nearly equal value; firstly, the Balanidae, or sessile cirripedes, which may be subdivided into two subfamilies, also very natural, the Balaninae and Chthamalinae; secondly, the Verrucidae, containing only one genus; and thirdly, the Lepadidae, or pedunculated cirripedes. Cirripedia having a carapace, consisting either of a capitulum on a peduncle, or of an operculated shell with a basis. Body formed of six thoracic segments, generally furnished with six pairs of cirri; abdomen rudimentary, but often bearing caudal appendages; mouth with the labrum not capable of independent movements; larva firstly uniocular, with three pairs of legs, lastly, binocular, with six pairs of thoracic legs. The Lepadidae, in one sense, may be taken as the type of their order; for they have undergone less morphological differentiation'; that is, they differ the least from the last larval stage, and seem to give the most general idea of a thoracic cirripede.
