248 SUBUNGULATA order ix 



raised trochlea and with articular surface for the cuboid. Fore and hind limbs very 

 short and with five digits. 



The Arsinoitheriidae are restricted to the Oligocene of Egypt. The skull 

 is of about the sanae size and very similar in form to that of the rhinoceros, 

 except that in these adults the nares are divided by a bony plate. The 

 high horns placed on the nasals recall those of the Titanotheriidae. The 

 ascending ramus of the lower jaw is very high and narrow. The teeth are 

 very compact and pass gradually from the chisel-shaped incisors to the fourth 

 premolar. The upper premolars have a straight ectoloph and an oblique 

 transverse ridge, the lower ones consist of two small strongly compressed 

 crescents. They are on the whole very short and differ considerably in this 

 respect from the molars. The molars consist of two V-shaped crescents, 

 whose anterior branch forms a very sharp edge, whereas the posterior one is 

 a broad, high, somewhat oblique backwardly directed ridge. When worn 

 down by grinding, this becomes in appearance an entoloph. The lower molars 

 recall those of Coryphodon, the upper those of Uintatherium. The two posterior 

 teeth of the milk dentition are very like the molars. 



The bones of the extremities are extremely stout. The scapula is broader 

 than high, the humerus has a very large deltoid crest, but no entepicondylar 

 foramen. The ulna is much thicker than the radius and has a huge olecranon. 

 It rests partly on the lunar. The pelvis is distinguished by the extremely 

 large ilium. The femur, which is antero-posteriorly compressed, has one 

 large trochanter. The bones of the fore limb are more like those of Uinta- 

 therium, those of the hind limb like those of Elephas. The arrangement and 

 form of the carpals, tarsals and metapodials are practically the same as in 

 Elephas, only the astragalus differs in having an articular surface for the 

 cuboid. There is, at all events, a distant relationship between these forms 

 and the Proboscidea. 



The only known genus is Arsinoitherium Beadnell (Fig. 332) from the 

 Oligocene of Egypt, having for type species A. zitteli Beadnell. 



Suborder B. HYRACOIDEA.^ 



Incisors long, vertically placed, rodent-like ; the lower first and second incisors 

 chisel-shaped. Premolars more or less molariform. Molars ranging from bunodont 

 to lophodont, with four roots. Lower surface of the zygomatic arch has special arti- 

 cular surfaces for the lower jaw. Ascending ramus of the lower jaw very broad, 

 with slender coronoid process and a foramen behind the third molar. Humerus with- 

 out entepicondylar foramen. Extremities plantigrade or semidigitigrade. Manus with 

 four digits, pes with three. Carpus serial with freely articulating centrale. Astra- 

 galus distally truncated, with excavated trochlea and a deep, pit-like articular surface 

 for the inalleolus tibiae. 



The Hyracoidea were until very recently represented only by the small 

 forms of the genus Hyrax, which was at first associated with rodents on 



^ Adloff, P., Zahnsysteni von Hyrax. Zeitsclir. f. Morph. und Aiithrop., 1002. — Andrews, 

 C. ir.. Catalogue, 1906. Geological Magazine, 1908. — Brandt, J. F., Untersuchungen iiber die 

 Klippschliefer {Hyracc). Mem. Acad. Iniper. Sci. St - Petersbourg, 1869, 6 str., vol. xiv. — 

 Major, C. I. Forsyth, PUohyrax graecus from Samos. Geological Magazine, 1899. — Schlosser, M., 

 Saugetiere aus deui Oligocau von Agypten. Beitr. Palaont. Ost. -Uugaius und des Orients, 1911. 



