Dolphins and Porpotses. 31 
pean, have flat skulls, very long beaks with a great number of 
teeth, and the frontal bones forming a broad zone on the forehead. 
In the Acrodelphinz the frontal zone is narrower, and the teeth in 
the type genus have numerous accessory denticules apparently 
representing the serrations on those of the extinct Squalodon, a 
genus mentioned later. The Patagonian Argyrodelphis, of which 
the skull is shown in fig. 29, also belongs to this group. 
; In the family Delphinide are included all the existing 
Dolphins toothed Cetaceans which do not come under the defini- 
pe tion of the Physeteride, Ziphude, Platanistide, or 
Porpoises. Iniide. From the existing representatives of the first 
two the members of this family are distinguished by the general 
presence of teeth in both jaws, as well as by the characters of the 
skull, while from the two last they differ by the mode of articula- 
lave, 1y(- 
The Left Periotic (Petrosal) Bone of a Pilot-Whale (Globicephalus melas), 
to show the type characteristic of the Delphinide. The difference between 
this bone and the corresponding element in the Beaked Whales will be 
apparent by comparing this figure with the one on page 27. Natural size. 
tion of the ribs with the vertebra. There are only four or five ribs 
with double heads ; the costal cartilages are fully ossified at an early 
age; the petroso-tympanics (fig. 17), which differ in form from the 
corresponding bones of the Physeteride and Ziphiide, are united 
by ligament with the skull; and the blow-hole is situated on the 
right side, and has the horns of the crescent pointing forwards. 
The nasal bones are short ;' the skull has no crests ; and the teeth 
are smooth. 
The family is divisible into the subfamilies Delphinapterine 
and Delphinine, in the first of which all the cervical vertebra are 
free. In this are included only the Narwhal (Monodon) and the 
Beluga, or White Whale (Delphinapterus). In the second sub- 
family at least the first two cervical vertebre are united. It 
