(After Darwin.)

Sub-order I. Thoracica.

Carapace, either a capitulum on a pedicle, or an operculated shell with a basis. Body, formed of six thoracic segments, generally furnished with six pairs of limbs; abdomen rudimentary, but often bearing caudal appendages.

Fam. 1. Balanidae.

Sessile, without a peduncle ; scuta and terga (forming the operculum) provided with depressor muscles ; the rest of the valves immovably united together. Fam. 2. Verrucidae.

Sessile. Shell asymmetrical, with scuta and terga, which are movable, but not furnished with a depressor muscle. Fam. 3. Lepadidae.

Pedunculated. Peduncle flexible, provided with muscles. Scuta and terga, when present, not furnished with a depressor muscle. Other valves, when present, not united into a single immovable case.

Sub-order II. Abdominalia.

Carapace, flask-shaped ; body formed of one cephalic, seven thoracic, and three abdominal segments, the latter bearing three pairs of cirri, but the thoracic segments being without limbs.

Genus - Cryptophialus.

Sub-order III. Apoda.

Carapace, reduced to two separate threads serving for attachment. Body consisting of one cephalic, seven thoracic, and three abdominal segments, all destitute of cirri. Mouth suctorial.

Genus - Proteolepas.