CETACEA. 59 



malia, though they do not present so many different forms. At 

 the same time, it is true, that compilers like Lesson, who appear 

 not to have examined a single skull, have made many genera, 

 founded on very slight characters, and bring together species that 

 have very little relation to each other. 



For the purpose of more distinctly denning the species, it has 

 been found necessary to divide them into several groups, so as to 

 arrange them into what appears to be a more natural series, and 

 circumscribe the genera. 



SYNOPSIS OF THE SUBFAMILIES AND GENERA. 



A. Jaws tapering, the symphysis of the lower jaw short, not 

 half the length of the jaw. Dorsal fin generally distinct* 

 Pectoral fin ovate acute. Marine. 



a. Upper jaw toothless, lower jaw with only one or two teeth 



(which are often hidden in the gums) on each side. Beak 

 of the skull keeled on each side, the keel being sometimes 

 large, and forming a kind of refiexed wing on each side. 

 Head with a short beak. Hyperoodontina. 



1. HYPEROODON. The beak of the upper jaw with a large 



erect wing-like expansion in front of the blowers ; lower jaw 

 with two rudimentary teeth in front. 



2. ZIPHIUS. Beak of upper jaw keeled on each side; lower jaw 



broad, bent down in front, with large compressed teeth in 

 the middle of each side. 



3. DELPHINORHYNCHUS. Beak of upper jaw keeled on each 



side ; lower jaw nearly straight, with two or three small, rudi- 

 mentary, conical teeth in the middle of each side. 



b. Upper and lower jaw with few or deciduous teeth. Wings 



of the maxillary bones expanded and shelving downwards. 

 The beak short, defiexed. Forehead convex. Head round- 

 ed, without any beak. Monoceratina. 



* Lower jaw toothless. 



4. MONODON. Upper jaw of males with one or two very long, 



projecting, spirally twisted tusks. Dorsal none. 



** Upper and lower jaw with conical, early deciduous teeth. 



5. BELUGA. Dorsal fin none. 



