lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



Whales lose their hair covering because it ceases to be of use ; at 

 most some few degenerated vibrissse remain/ 



It holds good for the cetacea as for other groups of mammals that 

 the most primitive forms have much less brain than the later ones; 

 in the highest whales the brain is extremely well developed. 



It likewise holds good for the cetacea as for others that the earlier 

 forms are smaller than the later, though dwarfs may at any time be 

 developed. Ordinarily whales increase noticeably in size as they 

 become more highly developed ; the highest forms have reached 

 gigantic proportions. 



Judging by their greater or less resemblance to the Hysenodonts 

 the cetacea are mutually related essentially as follows : ° 



Cetacea. 



I. The number of teeth is not more than typical [44]. Braincase 

 not telescoped, not shortened. 

 Archasoceti, 

 Zeuglcdontidae. 



Protocetus, Prozeuglodon, Zeuglodon. 

 II. The number of teeth is or has been more than typical. Brain- 

 case telescoped, shortened. 



A. Nasal bones forming a roof over hinder part of nasal 



cavity. Maxillary not covering frontal. 

 Mystacoceti. 

 Balaenidae. 



Bal^nini : Balcena, N eobalcona. 

 Bal^nopterini : Rhachionectes, Plesiocetus, 

 Cetotherium, Balcenoptera, Megaptera. 



B. Nasal bones pressed into fore wall of braincase, not or 



scarcely forming a roof over any part of nasal 

 cavity. Maxillary covering frontal. 

 Odontoceti. 



1. Teeth not alike, the most posterior less simply 



formed than the most anterior. 

 Squalodontidas. 

 Agorophius, Squalodon, Neosqiialodon, 

 Prosqualodon. 



2. Teeth now or formerly alike, simple in form. 



a. Temporal fossa large, not covered over by 

 frontal and maxillary ; zygomatic pro- 

 cess of the squamosal heavy, primitive 

 in form. 



