_Fossil forms._—Remains of a Cetacean from the Pleistocene of South America were referred by Bravard to _Pontoporia_, but they have been regarded by other writers as indicating a distinct genus, for which the names _Palæopontoporia_ and _Pontistes_ have been proposed. The Upper Tertiary European genera _Champsodelphis_ and _Schizodelphis_ are generally referred to the present family. The former has wide transverse processes to the lumbar vertebræ, as in _Inia_, while the teeth also resemble those of that genus. In _Schizodelphis_ the form of the rostrum presents a great resemblance to that of the Delphinoid genus _Steno_, but the symphysis of the mandible is relatively longer. A number of fossil Cetaceans from the Miocene of the United States, such as _Priscodelphinus_, _Lophocetus_, _Ixacanthus_, _Rhabdosteus_, etc., are referred by Professor E. D. Cope to this family. _Agabelus_, from the same deposits, is an apparently allied, but toothless type. _Family_ DELPHINIDÆ. Teeth usually numerous in both jaws. Pterygoid bones short, thin, each involuted to form with a process of the palate bone the outer wall of the post-palatine air-sinus. Symphysis of mandible short, or moderate, never exceeding one-third of the length of the ramus. Lachrymal bone not distinct from the jugal. The anterior facet on the periotic (Fig. 96) for articulation with the tympanic deeply grooved; and the posterior tympanic surface of the same bone comparatively narrow, with its ridge for articulation with the free border of the tympanic ill-defined, and situated close to one edge. Transverse processes of the dorsal vertebræ gradually transferred from the arches to the bodies of the vertebræ without any sudden break, and becoming posteriorly continuous serially with the transverse processes of the lumbar vertebræ. Anterior ribs attached to the transverse process by the tubercle, and to the body of the vertebra by the head; the latter attachment lost in the posterior ribs. Sternal ribs firmly ossified. External respiratory aperture transverse, crescentic, with the horns of the crescent pointing forwards. A very large group, closely united in essential characters but presenting great modifications in details. The different types are mostly so connected by intermediate or osculant forms that there are great difficulties in grouping them into natural subfamilies. Even the formation of well-defined genera is by no means satisfactory in all cases. They may, however, be divided, perhaps artificially, into two groups. _Group A._—Head rounded, without distinct rostrum or beak. Rostrum of skull about as long as cranial portion.