422 ORDERS OF MAMMALIA. 



cetoides of the Middle Eocene (Jackson Beds) of the United 

 States, which attained a length of seventy feet. 



By Professor Huxley, Zeuglodon is regarded as intermediate 

 between the true Cetaceans and the Carnivorous family of the 

 Seals. On this point, this eminent naturalist remarks : "The 

 skull of this great Eocene sea-monster, in fact, shows, by the 

 narrow and prolonged interorbital region ; the extensive union 

 of the parietal bones in a sagittal suture ; the well-developed 

 nasal bones ; the distinct and large incisors implanted in prae- 

 maxillary bones, which take a full share in bounding the fore- 

 part of the gape ; the two-fanged molar teeth with triangular 

 and serrated crowns, not exceeding five on each side in each 

 jaw ; and the existence of a deciduous dentition, its close re- 

 lation with the Seals. While, on the other hand, the produced 

 rostral form of the snout, the long symphysis, and the low cor- 

 onary process of the mandible, are approximations to the 

 Cetacean form of those parts." 



The genus Squalodon is nearly related to Zeuglodon, but the 

 teeth are more numerous ; and the double-fanged molars are 

 more compressed and pyramidal in form. " The nasal bones 

 are very short, and the upper surface of the rostrum presents 

 the groove, filled up during life by the prolongation of the eth- 

 moidal cartilage, which is so characteristic of the majority of 

 Cetaceans " (Huxley). The species of Squalodon all belong 

 to the Miocene and Pliocene Tertiary. 



The genus Saurocetes has been founded for the reception of 

 another Zeuglodont, in which there were double-fanged teeth 

 with conoid crowns. The remains on which this genus are 

 based, are from strata of Tertiary age, near Buenos Ayres, and 

 they indicate an animal much smaller than the true Zeuglodons. 



Lastly, it would appear probable that the genus Balcenodon^ 

 founded upon teeth from the Red Crag (Pliocene), is really re- 

 ferable to this family, and probably to the genus Squalodon. 

 In part, however, teeth of Ziphioid Whales have also been in- 

 cluded under this title. By Owen Balanodon is regarded as 

 comprising teeth of a Cetacean nearly allied to the living 

 Sperm Whale. 



