PLATANISTIDE 259 
Inia.\—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. Vertebre: C 7, D 13, L 3, C 18; total 
41. Transverse processes of lumbar vertebra very broad. Sternum 
short and broad, and consisting of a single segment only. Dorsal 
fina mere ridge. The long cylindrical rostrum externally furnished 
with scattered, stout, and crisp hairs. One species only is known, 
L. geoffroyensis, about 7 feet in length, inhabiting the upper Amazon 
and its tributary streams. 
Pontoporia.2—Teeth 50 to 60 on either side of each jaw, with a 
cingulum at the base of the crown. Jaws very long and slender. 
Vertebre: C 7,D 10, L 5, C19; total 41. Transverse processes 
of the lumbar vertebrae extremely broad. Sternum elongated, 
composed of two segments, with four sternal ribs attached. Dorsal 
fin rather small, triangular, pointed. External respiratory aperture 
Fia. 89.—Pontoporia blainvillei. (From Burmeister.) 
transverse, crescentic. This genus connects the last two forms with 
the true Delphinide. 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. 
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 Palwopontoporia and Pontistes have been pro- 
posed. The Upper Tertiary European genera Champsodelphis and 
Schizodelphis are generally referred to the present family. The 
former has wide transverse processes to the lumbar vertebrae, as in 
Inia, while the teeth also resemble those of that genus. In Schizo- 
delphis 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, 
Txacunthus, Rhabdosteus, etc., are referred by Professor E. D. Cope to 
1 D'Orbigny, Nouv. Ann. Mus. Paris, vol. iii, p. 31 (1834). 
2 Gray, Zoology of Erebus and Terror, p. 46 (1846). 
