EASTMAN: TYPES OF FOSSIL CETACEANS. 91 



We have substituted the genus Microzeuglodon, instead of Zeuglodon, as the 

 initial member of the above series, in accordance with the author's most recent 

 suggestion, published since the table first appeared. The opinion of most modern 

 writers regarding the impossibility of viewing Zeuglodon as the ancestor of 

 Squalodonts is accepted by Abel, who announces further the following general 

 conclusions : — 



1. The genus Squalodon is not descended from Zeuglodon. 



2. The precursor of Squalodonts is to be sought for among small Archaeoceti, 

 probably in Microzeuglodon. 



3. The most primitive Squalodont known at present is Neosqualodon. 



4. Microsqualodon represents a lateral offshoot of Squalodonts, transitional 

 between the genera Acrodelphis and Delphinodon (which may be identical). 



5. Under Squalodontidae are comprised very heterogeneous types, which should 

 be clearly distinguished from one another. 



Figure A. 



Transverse section across basal portion of rostrum of Lophocetus as provided by accidental 

 fracture-line seen in Plate 1. X \. 



The more general features of the skull of Lophocetus have now been con- 

 sidered, and the relations they are presumed to indicate have been pointed out- 

 A brief reference may be made here to the illustrations of the type specimen, 

 before passing on to consider the series of cervical vertebrae preserved with the 

 skull. 



Plates 1 and 2 show respectively the dorsal and inferior aspects of the cranium, 

 photographed from the actual specimen, and reduced to one-half the natural size. 

 The two transverse fracture-lines appearing in the specimen, one slightly in 

 advance of the position of the antorbital notch (the prominence for which is not 

 preserved), and the other which forms the present termination of the muzzle, 

 have been utilized for preparing the cross-sections shown in Figures A and B. 

 In these will be noted the wide separation of the premaxillaries, these elements 



