IMiOZKUGLODON ATllOX. 
255 
The ventral surface of the ceiitnun bears two blunt ridges, se[)arated by a narrow 
groove. 
Comparison of these vertebne with those of I'rotocetm atciKm shows that a 
considerable alteration has taken place, and that there is mncli less similarity to 
the vertebne of a carnivore. The atlas oi Protocetiis is unknown, but in the axis tbe 
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 Profocetus 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 Profocetus. The atlas is similar to the imperfect 
specimen figured by Muller (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. os/ris, 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 Profocetus and Zeuglodou, both in structure and in time. 
Prozeuglodon atrox, sp. nov. 
[Plate XXL ; text-figs. 80-83.] 
Tgpe 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 GO cm. ; 
the length of the upper premolar series I8‘2 cm. 
Form. (& Loc. — Birket-el-Quruu beds (Middle Eocene): a valley about 12 kilometres 
W.S.W. of the hill called Gar-el-Gehannem (see map in Introduction). 
C. 9319. Skull with right ramus of mandible. The palatal region and base of the skull aia' 
imperfect, fn the up[)er 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. Oidy one molar is In siiit, and it is 
