246 CETACEA 



Suborder ARCILEOCETT. 

 Family ZEUGLODONTID^E. 



This group is formed to include certain extinct Cetacean-like 

 animals at present only known by more or less fragmentary por- 

 tions of their skeleton and teeth, and whose position and affinities 

 are, therefore, still subject to doubt. 1 



In the anterior part of both jaws the teeth are simple, conical, 

 or slightly compressed, and sharp pointed. The first three in the 

 upper jaw are distinctly implanted in the premaxillary bone, and 

 so may be reckoned as incisors. The tooth which succeeds, or the 

 canine, is also simple and conical, but it does not exceed the others 

 in size. This is followed by five teeth having two distinct roots 

 and compressed pointed crowns, with denticulated cutting-edges. 

 The dentition is therefore i f , c \, p and m = 36, resembling that 

 of some Seals. 2 General form of the skull elongated and much 

 depressed. Brain-cavity very small, and the skull between it and 

 the orbits elongated and narrow. Temporal fossae very large. A 

 strong sagittal crest. Rostrum long and narrow, differing from 

 that of other Cetaceans in the large extent to which the premaxillae 

 form the sides of the anterior extremity. Nasal bones elongated, 

 flat, and narrow, the opening of the anterior nares being over the 

 middle of the elongated compressed rostrum. All the cervical 

 vertebrae free. The characters of the dorsal vertebrae and mode of 

 articulation of the ribs appear to have resembled those of Platanista 

 rather than JBalcena, Physeter, or Delphinus. Lumbar vertebrae 

 with elongated bodies, low neural spines, and the transverse pro- 

 cesses placed low down on the bodies. Characters of the limbs 

 not known with certainty. 3 



All the known fossil remains belonging to the animals of this 

 group may be referred, provisionally at least, to the genus Zeuglodon, 

 so named because the first section of a molar tooth examined was 

 taken from the base of the crown, where it was beginning to divide 

 into the two roots, and looked like two single teeth "linked or 



1 In a recent memoir Professor D'Arcy Thompson has brought forward some 

 arguments to show that the Zeuglodonts have no direct affinities with the Cetacea, 

 but have on the other hand the strongest possible relation with the Pinnipede 

 Garni vora. ' ' On the Systematic position of Zeuglodon, " Studies from tJie Museum 

 of Zoology, Dundee, vol. i. No. 9, 1890. 



2 An appearance in one specimen has been described by C. G. Cams as in- 

 dicating a vertical succession of the teeth, but the evidence upon which this rests 

 is by no means satisfactory, and appears to admit of another explanation. 



3 A mutilated humerus of Zeuglodon cctoides has given rise to many con- 

 jectures, appearing to some anatomists to indicate seal-like 'freedom of motion 

 at the elbow-joint, while to others its characters appear to be truly Cetacean. 



