8 SYSTEMATIC PALEONTOLOGY 



sponding tooth, but was obtuse, and furnished with a longitudinal ridge 

 on each side at the base of the crown. The surface of the enamel is 

 rugose, more minutely on one side than on the other. The tooth is 

 considerably curved. While the enamel is polished the fang is rough- 

 ened and opaque. 



Total length on middle 1 m 10.5 lines (48 mm,) 



Length of crown 



Width at base of crown 4.5 lines (9 mm,) 



Width at middle of fang 5,25 lines (10,5 mm.)" 



Occurrence. — Calvert Formation. Charles county, near the Patux- 

 ent river. 



Collection. — Philadelphia Academy of Natural Sciences. 



Family PLATANISTIDAE. 



The teeth are undifferentiated, conical and single-toothed; the pre- 

 maxillary is without teeth; the nose is extended into a long and slender 

 rostrum and in the lower jaw the symphysis is very long. Zittel says 

 that it is at least half as long as the jaw. The cervical vertebrae are all 

 separate and the ribs, except the most posterior, are two-headed, Note- 

 worthy living members of this group are Platanista of the Ganges which 

 is entirely fluvatile in its habits, never going into salt water, and 

 Pontoporia of the South American coast which is found near the mouth 

 of the La Plata river but has never been found in the fresh water of the 

 river. This last form serves as a connecting link in habits between the 

 Platanistidae and the succeeding family which is confined to salt 

 water. Most of the fossil forms of Odontoceti described from Mary- 

 land belong to the Platanistidae. 



Cope has given the following scheme ^ for the determination of the 

 genera of the family Platanistidae: 



I, Teeth with roots extended transversely. 



Teeth with lateral basal lobes; lumbar diapophyses wide Inia. 



II. Teeth with cylindrical roots. 



a. Caudal vertebrae plano-convex. 



No caudal diapophyses Cetophis. 



aa. Caudal vertebrae plane. 



'Amer. Nat., vol. xxiv, 1900, p. 603. 



