CLASSIFICATION OF VERTEBRATA 44 



Gfeomyidae. Nearctic and neotropical. 

 Geomys, Dipodomys. 



Dipodidae. Periarctic and Ethiopian. 

 Pedetes, Dipus. 



1 1sehyromys. Eo- and Miocene, North America. 



3. Order Cetacea (Linne), Cuvier. Anterior limbs trans- 

 formed into paddles ; posterior limbs lost. Tail long, with a 

 horizontal fluke. 



Teeth, if present, without enamel ; monophyodont. 



Teats inguinal. Placenta diffuse, non-deciduous. Cosmo- 

 politan. About 150 recent species. 



1. Sub-order AECHAEOCETI, Elower. All the ribs 

 with capitulum and tuberculum. 



Posterior teeth two-rooted. Skull symmetrical. 



Zeuglodon. Marine. Eocene of Alabama, Europe and 

 New Zealand ? 



2. Sub - order ODONTOCETI, Gray. Posterior ribs without 

 capitulum. 



All the teeth one-rooted. Skull asymmetrical. 

 Since the Miocene epoch. 



Squalodontidae. Squalodon. Marine, Mid- Tertiary of Europe, 

 North America, Australia. 



Platamstidae. Platanista, Ganges. 



Inia, Amazon. Pontoporia, La Plata. 

 Delphinidae. Since the marine Pliocene, cosmopolitan. 



Delphinus, Phocaena, Orca, Monodon, etc. 

 Physeteridae. Since the Miocene, marine. 



Physeter, Ziphius, Mesoplodon, etc. 



3. Sub-order MYSTACOCETI, Gray. Most ribs without 

 tuberculum. 



Teeth absent. Whalebone. Skull symmetrical. 

 Cosmopolitan, marine, since Miocene. 

 Balaenidae. Balaena, Balaenoptera, etc. 



4. Order Sirenia, Illiger. Anterior limbs transformed into 

 paddles, occasionally hyperphalangeal, namely, four phalanges. 



Posterior limbs vestigial or lost. 

 Tail long, with a horizontal fluke. 

 Teeth with enamel. Teats pectoral. 

 Placenta zonaris, non-deciduous. 



