1890.] The Cetacea. 605 
in proportions, and a long slender body. The first sternal seg- 
ment is T-shaped, and the ribs are slender, compressed, and 
mostly two-headed. The paddles are unknown. Other species 
of the genus are found in the Miocene beds of Maryland. The 
species of the remaining five genera have been found thus far 
only in the Miocene of North America. Nineteen species of 
Platanistidze have been described from the latter region. 
FIG. 2.—Priscodelphinus grandaevus Leidy, erteb a, from side; 4, from 
below. Original; from Miocene of Cumberland County, N. J- ~ One-third psi size. 
One line of modification observable in the extinct genera is 
towards the extreme which is seen in Rhabdosteus Cope. Here 
the muzzle reaches an extraordinary elongation, and for the 
greater part of its length forms an edentulous cylinder, which re- 
sembles the beak of the sword-fishes. The few teeth which remain 
at the base of the muzzle are like those of Platanista, with roots 
compressed so as to be longitudinal, and crowns com so 
as to be transverse, to the axis of the skull. The R./atiradir Cope 
(Fig. 4.), is not uncommon in the Miocene beds of Maryland. Its 
