38 



THE QUARTERLY REVIEW OF BIOLOGY 



these zeuglodonts retain their normal 

 mammalian relationships ; the facial region 

 is elongated without overlapping of the 

 bones. The braincase is narrow and 

 elongate, and not shortened antero-posteri- 

 orly as in living whales, for all have a 

 remarkable elongated intertemporal con- 

 striction and large temporal fossae. The 

 parietals are normal in their relation to 

 other bones and meet on the mid-line to 

 form a sagittal crest. The exoccipitals 

 are already extended laterally, and a 

 lambdoid crest is developed. The articu- 

 lar surface on the zygomatic process for 

 the lower jaw tends to assume the peculiar 

 vertical position of true Cetacea. All 

 known zeuglodont skulls have a flattened 

 forehead and a broadened supraorbital 

 process of the frontal, extended laterally 

 beyond the jugal portion of the zygomatic 

 arch, and arched at the extremity. The 

 nasal bones are elongated and do not 

 encroach upon the frontals, but lie almost 

 wholly in front of the level of the anterior 

 margins of the supraorbital processes. 

 The posterior portion of the nasal cavity 

 is relatively undisturbed, and turbinal 

 bones are present. The opening leading 

 to the nostrils has been moved backward 

 to the level of the first upper premolar, 

 about halfway to the orbit. The proxi- 

 mal end of the maxillary abuts against the 

 supraorbital process of the frontal su- 

 periorly and inferiorly projects backward 

 below the latter to accommodate the 

 posterior molars. The premaxillary has 

 an ascending process which does not reach 

 the frontal, but terminates behind the 

 antorbital foramen (above Pm 2 or Pm 3 ) 

 and anteriorly is conspicuously extended 

 beyond the extremity of the maxillary. 

 Apparently the mouth was used mainly as 

 a pair of forceps, with long, narrow, beak- 

 shaped rostrum, in which the anterior 

 teeth are widely spaced. The incisive 

 foramina were eliminated by the linear 



contact of the premaxillaries along the 

 mid-line. The palatines do not extend 

 forward beyond the level of the posterior 

 premolar, but the bony palate is prolonged 

 backward by outgrowths of the palatines 

 and pterygoids. The tympanic bulla has 

 already acquired an involucrum. If our 

 interpretation of the zeuglodont skull 

 is correct, a somewhat greater use was 

 made of that part of the tooth row which 

 serves for grasping food than of that which 

 serves for grinding, or shearing, and 

 consequently the incisors and anterior 

 cheek teeth increased in size. The pre- 

 molars became heavier, with higher 

 crown points, but the molars were 

 weakened, and the second upper molar 

 lost its predominance. The cheek teeth 

 of later zeuglodonts have several accessory 

 cusps on their anterior and posterior cut- 

 ting edges. The earlier zeuglodonts have 

 premolars and molars with vestiges of the 

 inner portion of the crown and a reduced 

 postero-internal cusp. The later zeuglo- 

 donts have lost the last upper molar, and 

 the remnant of the postero-internal cusp 

 disappeared with the third root. 



So far as known to the writer, no fossil 

 Archaeoceti have been found in the Lower 

 Eocene, though it is not unlikely that a 

 zeuglodont, Pappocetus lugardi, recently de- 

 scribed by Andrews (192.0) will eventually 

 prove referable to that period. This 

 small species was found in the Ombialla 

 District of Southern Nigeria in hard pyri- 

 tous clay and is represented by portions of 

 two left mandibles belonging to immature 

 individuals, for the last molars are not cut 

 in either specimen. The mandibles of 

 this zeuglodont apparently possessed the 

 full eutherian dentition, with 3 incisors, 

 1 canine, 4 premolars, and 3 molars in each 

 lower jaw, and it is especially interesting 

 on account of the carnivore-like characters 

 of the cheek teeth. The premolar-molar 

 series, with the exception of the first lower 



