Teeth 2, in the middle of the sides of the lower jaw. Teeth (of male) very long, strap-shaped, produced, arched obliquely, truncated at the end, with a conical process on the front of the terminal edge. Lower jaw weak, very slender in front. Symphysis elongate. 1. Dolichodon Layardii. B.M. Ziphius Layardii, _Gray_, _l. c._ p. 353, fig. 72. Dolichodon Layardii, _Gray_, _Synops. Whales & Dolph._ p. 10. Inhab. Cape of Good Hope (_H. Layard_). 4. NEOZIPHIUS. Teeth 2, in the front of the lower jaw, with a compressed, short, triangular crown. Lower jaw strong, rather narrow in the middle, and suddenly tapering in front of the tooth. Symphysis to the back edge of the teeth. 1. Neoziphius europæus. Dioplodon europæus, _Gervais_, _Ostéog. Cét._ t. 24 (skull). Inhab. Mediterranean. 5. DIOPLODON. Dioplodon, _Gray_, _l. c._ pp. 327, 355; _Synops. Whales & Dolph._ p. 10. Teeth 2 or 4, conical, in the middle of the sides of the lower jaw. Lower jaw broad behind, suddenly contracted in front. Symphysis moderate, not reaching halfway to the teeth. 1. Dioplodon sechellensis. Ziphius sechellensis, _Gray_, _Synops. Whales & Dolph._ t. 6. f. 1, 2 (skull). Dioplodon sechellensis, _Gray_, _Cat. S. & W._ p. 355; _Synops. Whales & Dolph._ p. 10, t. 5. f. 4; _Ann. & Mag. N. H._ 1870, vi. p. 343, fig. (skeleton); _Gervais_, _Ostéog. Cét._ t. 25 (skull). Dioplodon densirostris, _Gervais_, _Zool. Paléont. Franç._ t. 43. f. 3-6. [Illustration: Fig. 11. _Dioplodon sechellensis._] Inhab. Seychelles. Mus. Paris. Lord Howe’s Island (_Krefft_). The form of the lower jaw gives a very peculiar appearance to the skeleton. The cervical vertebræ are united together by their bodies and large dorsal spines, the latter forming a thick conical process. The bodies of the dorsal vertebræ are very small, enlarging in size towards the tail; they are thirty-six in number. The four terminal caudal ones are very small, forming a kind of cylindrical process. There are eight chevron bones. The thoracic cavity is small. There are twelve ribs on each side. The dorsal processes of the first eighteen vertebræ have an anterior basal process, which becomes gradually smaller. Upper arm-bone very slender, slightly curved; the lower arm-bones moderate, straight, parallel to each other, and rather longer than the upper arm-bone. The ribs very broad at the upper end, and gradually tapering towards the chest, where they are nearly cylindrical.