1. An account is given of the external and internal anatomy of a new species of the genus Baccalaureus.
2. The animal has a well-developed oral cone, consisting of an anterior labrum, paired mandibles, and paired maxillae. The histology of the gut, both in the segmented body and in the lateral coils, is described in detail.
3. A typical maxillary gland is present.
4. There are supra-oesophageal ganglia, circum-oesophageal commissures, and a short median ventral nerve-cord.
5. All the specimens are hermaphrodite. The ovary consists of a median bridge above the gut and branches in the lateral coils. Yolk-glands also are present. The testes fill the proximal parts of the appendages of the first three free thoracic segments. The spermatozoa are filiform, and are ejected in bundles.
6. Fertilization takes place in the lumen of the mantle coils or in the oviduct. Development as far as the nauplius takes place in the former, but the mode of liberation of these larvae has not been ascertained.
7. The characters of the nauplius are compared with those of other members of the Lauridae.
8. Previous work on the anatomy of the genus is discussed, and a reinterpretation of the results suggested.