BRAIN OF THE ZEUOLODONTIDiC, 617 



certain different Zeuglodont species. The species Zeuglodon osiris 

 Dames, 1894, was originally known from its lower jaw and certain 

 other skeletal remains. Stromer (1903) correctly identified the 

 skull of this creature, having in his possession an almost complete 

 head. In a later paper, however, Stromer (1908) has caused con- 

 fusion by referring an entirely different Zeuglodont to the same 

 species. It became necessary, therefore, to discover which form 

 actually was Zeuglodon osiris and, working with this information, 

 to arrange our series. 



In this matter two lines of evidence have substantiated our 

 findings. Elliot Smith (1903) described an imperfect endo- 

 cranial cast (M. 8150) which was known to have come from 

 a skull (M. 8150) determined as Zeuglodon osiris Dames by 

 Dr. Andrews in Egypt at that time. Fortunately, casts both of 

 the cranial cavity and of the skull itself were amongst the British 

 Museum material. In addition there were two skulls in the 

 Museum, both of which were termeA Zeuglodon osiris. A more 

 intimate survey of these two skulls (M. 10228 and M. 10173) has 

 rendered necessary their separation into two different species. 

 Further, by means of the matrix in which they are embedded, 

 Dr. Andrews is able to recognise them as probably coming from 

 two entirely different beds of the Middle Eocene epoch. The 

 first (M. 10228) possesses the same characters as M. 8150, and is 

 actually Zeuglodon osi7'is Dames (see text-fig. 14) from the Qnsr- 

 el-Sagha Series. These two skulls (M. 8150 and M. 10228) con- 

 form entirely to the description of that type given by Stromer 

 (1903). 



This primary orientation having been achieved, it became 

 api)arent that the second skull (M, 10173), hitherto classed 

 indiscriminately as Zeuglodon osiris, Avas not Zeuglodon osiris but 

 another form altogether. The matrix in which it is embedded 

 shows that it probably comes from the Birket-el-Qurun Series 

 (Operculina-Nummulite beds). Its characters are intermediate 

 between those of Zeuglodon osiris of the Carolia beds and Frozeu- 

 glodon airox Andrews (M. 9266) from the Ravine beds. The 

 endocranial casts confirm these facts ; indeed, it was the serial 

 conformity of the casts which led us to a re-examination of the 

 osteological features. 



Therefore, three of the endocranial casts here described come 

 from skulls whose osteological features are known. Further, as 

 a group, these three skulls and their casts may be conveniently 

 regarded as a phyletic series. In view of this fact, Dr. C W. 

 Andrews has kindly written an account of the osteological 

 features of the new form (M. 10173), which we will call provi- 

 sionally Zeuglodon inter mediiis, sp. nov., and has stated its geo- 

 logical liorizon to have probably been the Birket-el-Qurun series 

 {vide p. 35, ' The Topography and Geology of the Fayum Province 

 of Egypt,' H. J. L. Beadnell, Survey Department, Cairo, Egypt, 

 1905). 



