III. Pectoral fin elongate, truncated on the inner side; fingers 4, subequal, more or less elongate.—Agaphælidæ, Megapteridæ, Physalidæ, Balænopteridæ.
By the adhesion or non-adhesion of the cervical vertebræ, thus:—
1. Atlas distinct, the other six cervical vertebræ united by their bodies and spines into a single mass.
Mysticetes.
Denticetes.
- Catodontidæ.
- Grampidæ.
2. Atlas and cervical vertebræ all united into one solid mass.
- Balænidæ.
- Balænopteridæ.
- Physeteridæ.
- Hyperoodontidæ
- (?) Ziphiidæ.
3. The atlas, axis, and generally one or two other vertebræ united; the hinder ones sometimes free.
- Megapteridæ.
- Epiodontidæ.
- ? Ziphiidæ.
- Delphinidæ.
- Globiocephalidæ.
- Orcadæ.