ISqaalodoii and Zeayludon. 203 



throughout their length by the isthuinus, or whether they pro- 

 jected freely beyond it. Lateral cusps rather large. Ornament 

 as in Parasqualodon. 



Only species MeUi-^quaJodon harwoodi. Sanger. 



In discussing the atfinities of Prosqualodon, Lydekker says 

 that in the structure of the nasals the South American genus 

 is more generalised than Squalodon, while in the character of 

 the teeth it is more specialised. ' As we know only the teeth 

 of our Australasian genera, and these imperfectly, we cannot say 

 whether or not they were in. advance of the specialisation of 

 the skull. 



Geologists are as yet undecided as to the age of the Patagonian 

 tertiaries. Those in the United States, and most of those in 

 Europe, refer to the Santa Cruz beds which yielded Prosqualodon 

 to early miocene or perhaps oligocene. Von Ihering, who has 

 spent many years on the task, and is familiar with the recent 

 mollusca of South America, still tights vigorously for their 

 eocene age, and is, I think, working on correct lines. 



The New Zealand Kekenodon is said by Hector to be eocene, 

 but the matter is still in doubt. As regards the beds in Southern 

 Australia which have yielded Squalodonts, opinions vary be- 

 tween eocene, oligocene and miooene. At present those which 

 have yilded Prosqualodon are spoken of merely as Janjukian. 

 The polyzoal limestone of Mount Gambler is, of course, prac- 

 tically devoid of mollusca, and its relationships are consequently 

 not eas.y to settle, but they appear to lie rather with Muddy 

 Creek, Avhich is Balcombian, than with Janjukian. The beds of 

 the Murray River cliffs, whence Sanger's type came, are 

 generally regarded as Janjukian, but variations may occur in 

 such a great range of outcrop. 



There are differences of opinion as to the sequence of these 

 two subdivisions of the Barwonian system, my view being that 

 Janjukian is the older. 



LITERATURE. 



Andrews, C. W. (1906. — Descriptive catalogue of the tertiary 

 vertebrata of the Fayum, Egypt, etc. British Museum. 



Carus, G. C, 1850. — Das Kopfskelet des Zeuglodon hydrarchos. 

 Nov. Act. Ac. Caes. v. 22, pt. 2, pi. 39a, 39b. 



