CETACEA. 271 



found with undoubted Zeuglodont remains, are probably correctly identi- 

 tifil. The skull is elongated and much depressed, and notwithstanding 

 the extent of the brain-case, its cavity is very small. The frontal bones 

 are very short and broad. The nasal bones are separate, antero-posteriorly 

 elongated elements roofing the nasal chamber, which opens externally in a 

 single orifice on the top of the rostrum at about its middle. The pre- 

 muxilku form an unusually considerable length of the end of the snout. 

 The symphysis of the mandible is very long. The teeth are considerably 

 spaced, fixed in distinct sockets, and with more or less enamelled crowns. 

 In the typical species there are three simple conical teeth in the pre- 

 maxilla, and a larger tooth of the same form occurs near the anterior end 

 of the maxilla ; then follow five larger teeth, also conical, but with more 

 compressed and longitudinally extended crowns notched or serrated on 

 the front and hind borders, and each implanted by two distinct roots 

 (fig. 158). Nine corresponding teeth occur on each side of the lower jaw. 



i. 3, c. 1, pm. + m. 5 



The dental formula is thus commonly expressed : ^-^ . 



i. 3, c. 1, pm. + m. 5 



Successional teeth have not been observed with certainty. The cervical 

 vertebrae are not shorter than the anterior dorsals, and none are fused 

 together. The lumbar vertebrae are considerably elongated, while the 

 caudals are short. The somewhat expanded scapula exhibits a large spine 

 and a comparatively small coracoid process. The humerus tapers at its 

 distal end, where slightly convex facettes for the radius and ulna can be 

 distinguished. The supposed dermal armour, known only by fragments, 

 consists of irregular, smooth, bony tesserse, more or less fused together. 

 It seems to resemble the rudimentary dermal armour of the existing 

 Phoccena. The skull of the typical species, Zeuglodon cetoides, from the 

 Eocene of Arkansas and Alabama, U.S.A., attains a length of nearly a 

 metre. More fragmentary specimens, to which other specific names have 

 been given, are known from Louisiana and Mississippi, U.S.A.; from the 

 Barton Clay of Hampshire ; from the Eocene of France, Germany, the 

 Caucasus, and Egypt ; from Malta ; and also from supposed Eocene 

 strata in South Australia and New Zealand. 



Sub-Order 2. Odontoceti. 



The typical skull of the toothed whales, or ODONTOCETI, had 

 already been developed, and the teeth had begun to multiply, 

 before the differentiated character of the dentition just described 

 in the Archaeoceti, disappeared. Prosqualodon, from the Marine 

 Patagonian Formation (supposed Miocene) of Chubut, Argen- 

 tine Republic, and Squalodon, from the Miocene and Pliocene 

 of Europe (probably also North America and Australia), bear 

 witness to this fact. 



