PHOZEUGLODON ATROX. 255 



The ventral surface of the centrum bears two blunt ridges, separated by a narrow 

 groove. 



Comparison of these vertebrae with those of Protocetus atavus shows that a 

 considerable alteration has taken place, and that there is much less similarity to 

 the vertebrae of a carnivore. The atlas of Protocetus is unknown, but in the axis the 

 peg-like odontoid and the relatively long centrum are characters approaching those 

 found in the Carnivora ; on the other hand, in Prozeuglodon the odontoid has already 

 become short and blunt, and the centrum is much shortened, as also are the transverse 

 processes ; at the same time, the high massive neural spine is retained. In the third 

 cervical, the great shortening up of the centrum in Prozeuglodon compared with the 

 same vertebra in Protocetus is most striking ; in this case also the transverse processes 

 are reduced, while the neural spine is moderately developed. Comparison with the 

 corresponding vertebrae of Zeiiglodon shows that the present species approaches much 

 more nearly to that genus than to Protocetus. The atlas is similar to the imperfect 

 specimen figured by Miiller (pi. xiii. figs. 1, 2), except that the ventral bar is not so 

 thick ; in both there is a hypapophysis. The odontoid process is more rounded than 

 in Zeuglodon, its upper surface showing very little trace of flattening, and therefore 

 differing widely from that of Z. zitteli as described by Stromer ; the neural spine 

 overlies the atlas, as described by Lucas. The third vertebra is shortened to about 

 the same degree as in Z. osiris, and possesses a fairly developed neural spine, said to 

 be absent in the corresponding vertebra in Z. cetoides. 



This genus in the structure of the skeleton, so far as known, does not throw any 

 new light upon the relationships of the Zeuglodonts to the Creodonts on the one hand 

 or to the Odontoceti on the other ; and its chief interest consists in its almost exactly 

 intermediate position between Protocetus and Zeuglodon, both in structure and in time. 



Prozeuglodon atrox, sp. nov. 



[Plate XXI. ; text-figs. 80-83.J 



Type Specimen. — A nearly complete skull with right ramus of mandible (described 

 above, and figured on PI. XXI.) ; Geological Museum, Cairo. 



This is the only species at present known. The length of the skull is 60 cm. ; 

 the length of the upper premolar series 18-2 cm. 



Form. & Loc. — Birket-el-Qurun beds (Middle Eocene): a vaUey about 12 kilometres 

 W.S.W. of the hill called Gar-el-Gehannem (see map in Introduction). 



C. 9319. Skull with right ramus o£ mandible. The palatal region and base of the skull are 

 imperfect. In the upper jaw the incisors and canine are represented by their alveoli 

 only ; the first premolar is just appearing, while the second, third, and fourth have high 

 secant crowns, the two latter possessing three roots. Only one molar is in situ, and it is 



