Dr. C. W. Andrews — Prozeuglodon atrox. 209 



would tend to generate a lateral subterranean movement, or squeeze 

 towards the land ; for resistance in that direction would always be 

 diminishing owing to the lessened pressure exerted by the risingland, 

 which would lower the density immediately beneath it. Some 

 evidence of such movements in former times ought to be found in the 

 strata of the earth, for actions of this sort must have taken place ever 

 since rain and rivers began their work upon the globe. 



lY. — J^OTE om A Model op the Skull and Mandible of 



PsOZEUaLODON ATROX, ANDREWS. 



By C. W. Andhews, D.Sc, F.R.S. (British Museum, Natural History). 



(PLATE IX.) 



DURING the last few years several papers have been published 

 which throw much light on the early history of the whales, 

 a matter about which there have been great doubt and difference of 

 opinion. Two important points appear to have been settled : first, 

 that the Zeugiodonts {Archceoceii) are descended from the primitive 

 group of land- carnivores, usually known as the Creodonta, and, 

 second, that the Toothed- whales ( Odontoceti) are really derived from 

 the Zeugiodonts. On this second point there may still be room for 

 doubt, although in the opinion of the present writer the evidence 

 brought forward by Professor Abel ' in several papers, is at least 

 sufficient to demonstrate the extreme probability that the Archseoceti 

 are really ancestors of the Odontoceti. The origin of the Baleen- 

 whales {Mystacoceti) is still obscure, but the fact that numerous true 

 teeth are found in the unborn young, points to the probability that 

 -these animals also may have originated from the same, or a closely 

 related stock as that from which the Odontoceti have descended. 



The series of forms linking the Zeugiodonts to the terrestrial 

 Creodonts has been discovered quite recently in the Middle Eocene 

 deposits of Egypt. The earliest type is from near the bottom of the 

 Lower Mokattam series (Middle Eocene) of Cairo : this animal, which 

 has been described by Professor E. Eraas - under the name Protocetus 

 atamis, is known from a nearly complete skull and some cervical 

 vertebrae. The skull, which is about 60 cm. in length, much resembles 

 in its general structure that of Prozeuglodon (see Plate IX) or 

 Zeuglodon, but has a rather more slender snout, with the nostrils 

 situated relatively farther forward than in the later forms. The full 

 Eutherian dentition (i. f, c. ■^, pm. -f-, m. f) is present. The secant 

 premolars and molars show no trace of the serration of their edges 

 so characteristic of the later Archseoceti, but are much like those 

 of a Creodont of the Hyaenodont group ; the third and fourth 

 premolars have large inner (third) roots, while the same seems to be 



^ " Eiue Staiumtypus der Delphiniden aus dem Miocaii der Halbinsel Taiuan": 

 Jahrb. der k.k. geol. Eeichsanstalt, vol. Iv, pt. 2 (Vienna, 1905), p. 375. 



" Die pliylogenetische Entmcklung- des Cetaceengebisses und die systematische 

 Stellung der Physeteriden " : Verhandl. d. deutsch. Zool. Gesellschaft, 1905, p. 84. 



^ " Neue Zeuglodonten aus dem unterem Mitteleocan vom Mokattam bei Cairo " : 

 Palaeont. Abhandl., n.s., vol. vi (1904), p. 199. 



DECADE v.— VOL. V. NO. V. 14 



