30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



ing .the measurements of these bones in the adult South African 

 skulls, while others are less. A detailed study of the skull and dental 

 characters shown by the series of fourteen Lado skulls of the Smith- 

 sonian African Collection, has been made to determine the variations 

 due to age, sex and the individual. With these variations in mind a 

 careful comparison has been made between this material and the nine 

 adult skulls from South Africa preserved in European museums, 

 together with measurements and photographs of the three skulls from 

 South Africa in the British Museum. The only valid difference in 

 skulls detected between the material from these two widely separated 

 localities is a greater depth to the dorsal concavity in the South Afri- 

 can specimens. This greater depth is due to the higher projection 

 of the lambdoidal crests of the occipitals above the fronto-parietal 

 plane of the cranium. A similar projection of the occipital crests 

 occurs in both Coelodonta and Diccros, but to a much greater degree, 

 being so marked as to be of generic importance. Ceratotherium has 

 the flattest dorsal profile of the living rhinoceroses. In the Nile race 

 the flatness reaches its extremity and gives this race the extreme of 

 specialization. There is little doubt but that the ancestral stock of 

 Ceratotherium possessed the high occipital crests of the Rhinocero- 

 tida generally, and that flatness shows specialization. The difference 

 of depth of the dorsal concavity, however, is only an average and not 

 an absolute character. In the adults from Lado it is 50 mm. or less, 

 while in the South African it is at least 60 mm., usually 65 mm. In the 

 immature Lado specimens it is much greater than in the adults, those 

 with milk dentition still in use showing depths ranging from 50 mm. 

 to 57 mm. The teeth of the South African specimens also show 

 greater size, the tooth row of adults averaging about 300 mm., while 

 in the Lado race their average is only 270 mm. 



The type skull of Ceratotherium simum cottoui has been examined 

 and carefully measured by the writer. It is that of an immature male 

 showing the last milk molar worn down to its roots and about to be 

 shed, and the last molar not yet erupted. The age of this skull is 

 practically that of number 164635, U. S. National Museum. It shows 

 decided peculiarities, however, and cannot be matched by any other 

 Lado skull. The nasal boss is extremely wide for so immature a male 

 and is equal to that of a fully adult animal. The nasal projection is, 

 however, short and normal for the age it represents. We have a great 

 number of individual variations to deal with in this species. It is 

 only by comparing minutely a large number of skulls that any real 

 skull characters may be discovered. The nine South African skulls 



