Revieios — R. Lydekher — Fossil Mammalia. 427 



present we possess only imperfect materials for study, are provision- 

 ally referred to the family Rhinocerotidce, namely : Hyracodon, Cadur- 

 coiherium, Jldmalodontotherium and Elasmotherium. Of these four 

 genera, one only ( Cadurcotherium) dates back to the Eocene period. 



Periptychus and JZdploconus are both Lower Eocene genera from New 

 Mexico in North America. They are characterized by the grooved 

 and ridged sculpture of the teeth. They form a part of the sub- 

 order Condylarthra, in which are placed a number of those primi- 

 tive Mammals having a bunodont or lophodont type of cheek- 

 dentition, foreshadowing both the Artiodactyla and Perissodactyla ; 

 there are usually five digits in both the manus and pes, the terminal 

 phalangeals being acuminate. The best-preserved example of the 

 family is the genus Phenacodus, of which a figure was given in the 

 Geological Magazine for February, 1886 (Plate II. p. 49). 



Under the suborder Amblypoda is placed the remains of the 

 genus Coryphodon, from the Lower Eocene of Harwich, Essex, and 

 from Dulwich, near London. It also occurs in the Eocene of France 

 and North America. 



Coryphodon was the largest of the early Eocene Ungulates, and the 

 relative smallness of its brain, together with its five-toed feet, which 

 resemble in structure those of the Dinocerata, indicate some affinity 

 to that group, which it also preceded. 



The section Dinocerata is included in the same suborder, and 

 completes the series of Eocene Mammals represented in the collection. 



We are indebted for our very perfect knowledge of the genera 

 Tinoceras and Dinoceras to Professor 0. C. Marsh, whose labours in 

 exploring the Eocene Tertiary deposits of the Wyoming Territory 

 have opened up an entirely new chapter in Tertiary paleontology. 



For a full account, with figures, of these interesting genera, see 

 the Geological Magazine for May, 1885, Decade III. Vol. II. pp. 

 212-228 (with 18 Woodcuts). 



The fore and hind limbs had feet with five well-developed toes, 

 each terminating in a hoof ; the femur and tibia were placed 

 vertically in a line, as in the hind-leg of the Elephant. The nasal 

 bones were elongated, having two small pre-nasal bones in front of 

 them; the animal does not appear to have been furnished with a 

 proboscis. 



The most striking feature is the skull, which is surmounted by 

 three pairs of rounded protuberances or horn-cores, which were pro- 

 bably enveloped in horny sheaths. There are no upper incisors, 

 but the upper canines are developed into large and powerful flattened 

 tusks, directed downwards, and protected on each side by the broadly- 

 expanded margin of the lower jaw. 



These early Eocene types have so important a bearing upon the 

 question of the derivation of our existing Mammalian fauna, that we 

 cannot but welcome every addition to our knowledge concerning 

 them, and we have to thank Mr. Lydekker for this further instal- 

 ment of his Catalogue, and to express the hope that we may soon 

 have it before us in its completed form. 



