_Platanista._[151]—Teeth about ³⁰⁄₃₀ on each side, set near together, rather large, cylindrical, and sharp-pointed in the young; in old animals acquiring a large laterally compressed base, which in the posterior part of the series becomes irregularly divided into roots. As the conical enamel-covered crown wears away, the teeth of the young and old animals have a totally different appearance. The rostrum and dentigerous portion of the mandible are so narrow that the teeth of the two sides are almost in contact. Maxillæ supporting very large, incurved, compressed bony crests, which overarch the nares and base of the rostrum, and almost meet in the middle line above. Orbits very small and eyes rudimentary, without crystalline lens. External respiratory aperture longitudinal, linear. Vertebræ: C 7, D 10, L 9, C 26; total: 52. A small cæcum. No pelvic bones. Dorsal fin represented by a low ridge. [Illustration: FIG. 88.—_Platanista gangetica._ (From Anderson.)] One species, _P. gangetica_, entirely fluviatile, being extensively distributed throughout nearly the whole of the river systems, not only of the Ganges, but of the Brahmaputra and Indus, ascending as high as there is water enough to swim in, but never passing out to sea. It is quite blind, and feeds on small fish and crustaceans, groping for them with its long snout in the muddy water at the bottom of the rivers. It attains the length of 8 feet.[152] _Inia._[153]—Teeth variable, from 26 to 33 on either side of each jaw; those at the posterior part with a distinct tubercle at the inner side of the base of the crown. Vertebræ: C 7, D 13, L 3, C 18; total 41. Transverse processes of lumbar vertebræ very broad. Sternum short and broad, and consisting of a single segment only. Dorsal fin a mere ridge. The long cylindrical rostrum externally furnished with scattered, stout, and crisp hairs. One species only is known, _I. geoffroyensis_, about 7 feet in length, inhabiting the upper Amazon and its tributary streams. _Pontoporia._[154]—Teeth 50 to 60 on either side of each jaw, with a cingulum at the base of the crown. Jaws very long and slender. Vertebræ: C 7, D 10, L 5, C 19; total 41. Transverse processes of the lumbar vertebræ extremely broad. Sternum elongated, composed of two segments, with four sternal ribs attached. Dorsal fin rather small, triangular, pointed. External respiratory aperture transverse, crescentic. This genus connects the last two forms with the true _Delphinidæ_. The only species, _P. blainvillei_, is one of the smallest members of the whole order, not exceeding 5 feet in length. It has only been met with at the mouth of the Rio de la Plata, near Buenos Ayres, and there is at present no evidence that it ascends into the fresh waters of the river. [Illustration: FIG. 89.—_Pontoporia blainvillei._ (From Burmeister.)]