1890.] The Cetacea. 609 
The DELPHINIDÆ are preéminently a modern type (Fig. 6). 
They display a tendency to the reduction of the rib heads, which 
is completed in the whale-bone whales, and the nostrils are far 
posterior, and the nasal bones mere tuberosities. The dentition 
differs within moderate limits; the killers, as the carnivora of the 
sea, having it powerfully developed, while in the grampus and 
Globiocephalus many of the teeth are shed. Monodon develops 
a large incisor with which it breaks the ice in Arctic regions. 
The genera differ as follows: 
I. Cervical vertebrze mostly distinct. 
a, Incisors not differentiated. 
Teeth few, caducous ; Delphinapterus! Lac. 
aa, Superior incisors of one side forming a straight tusk. 
Teeth few, deciduous ; Monodon Linn. 
II. Cervical vertebrae mostly coössified. 
A. Flippers short, with less than'twelve phalanges in 
the second finger. 
a, A dorsal fin. 
Teeth few; very robust; palate not grooved ; Orca Gray. 
Teeth medium, numerous, acute ; palate not 
rooved ; Lagenorhynchus? Gray. 
Teeth medium, numerous, acute; palate 
grooved ; Delphinus Linn. 
Teeth numerous; premaxillae elevated in 
front of nares; palate plane ;  Sagmatias? Cope. 
Teeth few, easily shed; Grampus Cuv. 
Teeth compressed, spatuliform ; Phocena Cuv. 
aa, No dorsal fin. 
Teeth numerous, not caducous ; Leucorhamphus” Lilly. 
Teeth flat, spatuliform ; Neomeris Gray. 
AA. Flippers long, falciform; index with twelve or 
. more phalanges. 
A dorsal fin; teeth few, caducous ; Globiocephalus Gray. 
7 Beluga Gray. 
8 Tursiops and Prodelphinus Gerv. 
? Dorsal fin unknown. 
10 Delphinapterus Less. nec Lacep. 
