30 Gude to Whales, Porpotses, and Dolphins. 
short and wide. From the next family the Platanistide differ by 
the slit-like form of the blow-hole, the presence of a cx#cum to 
the intestine, the development of a high crest on each maxilla 
(fig. 15), and by the teeth undergoing remarkable changes with 
age. The Susu, which grows to a length of 8 feet, is blind, and 
feeds by groping in the mud of the rivers for crustaceans and 
small fishes. It is represented by a stuffed specimen, a skeleton, 
and several skulls, some showing the thin, sharp young teeth, and 
others the thick, blunt ones of maturity. 
The second family, Inizde, includes the Amazonian Dolphin 
(Inia geoffroyensis), which grows to 7 feet, and the La Plata 
Dolphin (Pontoporia, or Stenodelphis, blainvillet), inhabiting the 
estuary of the Rio de la Plata, and scarcely exceeding 4 feet in 
length, together with a number of extinct genera. In both recent 
species the opening of the blow-hole is crescentic, there is no 
cxcum to the intestine, the upper jaw does not carry crests, and 
the transverse processes of the lumbar vertebree are very broad. 
The snout of Inia retains a number of scattered bristly hairs. In 
the La Plata Dolphin the beak is very long, with from 50 to 60 
pairs of teeth; and there is a back-fin which is wanting in both 
the Amazonian Dolphin and the Susu. The La Plata Dolphin 
(fig. 16) is represented by a coloured sketch and a plaster cast of a 
specimen taken in 1893 in the Bay of Monte Video, as well as by 
the skull and skeleton. Of the Amazonian species only the skull 
and skeleton are shown. 
The La Plata Dolphin has the cervical vertebree separate and 
the transverse processes of the lumbar vertebrie very broad, as in 
Inia, but the pterygoid bones of the skull are involuted, the sternal 
ribs (costal cartilages) are ossified, and the true ribs articulate with 
the vertebrae in the same manner as in the Delphinide. The extinct 
Pontistes is very close to Pontoporia (Stenodelphis), but larger. In 
both these genera the prenarial region of the skull, and also the 
shape of the nasal bones and the form of the zygomatic process, 
recall the corresponding regions in the Porpoise (Phocena). 
The two living species, together with the extinct Argentine 
genus Pontistes, constitute the subfamily Indidx ; in addition there 
are two extinct subfamilies, the Argyrocetine (with the genera 
Argyrocetus, Cyrtodelphis, Pontivaga, Ischyrorhynchus, and Champ- 
sodelphis) and the Acrodelphinee (with Acrodelphis and Hetero- 
delphis). The Argyrocetine, of which the type genus is from the 
Miocene of 8. Ameri¢a, although several of the others are Euro- 
