CETACEA. 



309 



but possess whalebone on the palate, feed on small marine animals, 

 nudibranchiate Molluscs and Medusae. The Dolphins, with their 

 uniform carnivorous dentition, feed on larger fishes ; the Sirenia, 

 which are intermediate, so far as their form is concerned, between 

 the Whales and Seals, are herbivorous. Fossil remains are found 

 in the older tertiaries. 



Sub-order 1. Cetacea carnivora (True Whales). Either with 

 conical teeth in the jaws or with whalebone on the palate. The 

 nasal apertures are placed on the forehead. The larynx projects 

 like a pyramid into the posterior nares. The mammfe are placed on 

 the inguinal region. The skin is devoid of hairs, and beneath it is 

 a thick layer of fat. The limbs are movable at the shoulder 

 joint only; their constituent bones are rigidly and immovably 

 connected. 



FIG. 689. Delphinus delphis (regne animal). 



Tribe 1. Denticete (Toothed Whales). Carnivorous Whales which 

 feed principally on fish, with conical teeth in both or only in one 

 jaw. Dentition monophyodont. Head of proportionate size. Nasal 

 apertures often united to a single semilunar opening. 



Fam. Delphinidae. Both jaws with similar conical teeth, but not always 

 armed along their whole length. Nasal apertures united to a semilunar 

 spiracle. Phoctena communis Less., Common Porpoise, four to five feet long 

 ascends the mouths of rivers, lives on Fishes. European seas. Beluga 

 (DelpMnapterus) leucas Gray, White Fish ; GloUoceplialus gloUceps Cuv., 

 Black Fish, North Atlantic Ocean ; Delphinus delpliis L., Common Dolphin 

 (fig. 689). 



Fam. Monodontidae (Narwhals). Upper jaw with only two anteriorly directed 

 teeth which in the female are small ; but in the male one of them (usually that 

 of the left side) becomes a colossal, spirally grooved tusk. The other small 

 teeth of both jaws fall out early. Monodon inonoceros L., Narwhal. North 

 Polar Sea, twenty feet long. 



Fam. Hyperoodontidae. With elongated beak-like snout, only one or two 

 fully developed teeth on each side in the lower jaw. Facial bones, especially 



