VERTEBRATA. 



255 



There are upwards of sixty genera for less than that number of 

 well-ascertained species ; Sowerby's whale has been placed in not 

 less than thirteen of them. Zeuglodontidse are found in the 

 Eocene and Miocene deposits of North America ; they differ from 

 all other Cetaceans in having molars with two fangs. Some of 

 the Cetacea attained a length of 70 feet. 



Bal&nopteridce Physeteridce. Delphinidee. 



(Fin- whales, or Physeter=Catodon Platanista. 



Eorquals). (Cachalot, or Inia. 



Megaptera. Sperm-whale). Delphinus (Dolphin). 



Physalus Monodontidce. (Grampus). 



Balaenoptera. .. Phocagna (Porpoise). 



Monodon (Narwhal). Gi obic ephai u / ( B o t- 



Balcenidce. Hyperoodontidce. tlenose). 



Balsena (Whale, or Ziphius. Beluga (white whale, 



Whalebone Whale). Hyperoodon. r white-fish). 



*Zeuglodontid(B. 

 *Zeuglodon. 



Order XI. SIRENIA. 



Body fish-like. Nostrils on the muzzle. Fore limbs only 

 fin-like. No sacrum. Pelvis rudimentary. A horizontal tail- 

 fin without bony rays. 



The Sirenia differ from the whales in having two kinds of teeth, 

 incisors and molars; in the position of the nostrils on the 

 snout ; in the fleshy lips, provided with short thick scattered 

 bristles : and in the pectoral mammae. They have also a third 

 eyelid and salivary glands. Their limb-bones are solid ; they 

 have no clavicles, and no external ear. Their pelvic bones 

 in their highest development " retain the size and shape of the 

 small contiguous costal arches.'' The stomach is large, and the 

 caecum is of moderate size. The diaphragm is exceedingly 

 oblique. 



In the dugongs the males are furnished with two large incisors 

 in the upper jaws ; in the female they are arrested in their growth 

 without cutting through the gum, and they remain through life 

 concealed in the premaxillaries. 



The Manatidse (the only family) are herbivorous ; one of its 

 species (Manatus americanus) lives almost exclusively on Pistia 

 stratiotes ; another species (Rhytina stelleri), of large size, is now 



