INDUSTRIAL PROGRESS DURING THE YEAR 1876. clxxiii 



These forms have quite a characteristic combination of characters : 

 tiie skull of the known species has superficial resemblance to that 

 of a bear ; the incisor teeth were much like those of rodents, beino- 

 two in number in each jaw, and apparently reproduced by gradual 

 growth from their bases ; the molars resembled those of the pachy- 

 derm ungulates ; the feet were pentadactyle ; the scaphoid and 

 lunar were separate from each other ; the digits provided with 

 claws. This unusual combination of characters can not be recon- 

 ciled with the accepted diagnostic marks of any of the existing or- 

 ders ; and either the generally admitted definitions or the orders of 

 the present age will have to be modified to include these extinct 

 forms, or the forms thus left must remain, as indicated by Professor 

 Marsh, as representatives of a distinct order. The brain, as in the 

 Dinocerata^ was very small in comparison to the bulk of the animal, 

 although (as might have been premised from the size of the animal) 

 much larger in proportion than in the latter. The species known 

 were smaller animals than those of the group just noticed, the best 

 known species of Tillotheriwn being only about half or two thirds 

 the size of the common South American tapir. 



In the. same Eocene period, and perhaps contemporary with the 

 last, lived a horse-like animal of a still more generalized type than 

 any of those which had previously been made known. This animal 

 was about as large as a fox, but somewhat more robust in its pro- 

 portions ; the feet had well-developed digits four in front ; behind, 

 three perfect, and a fourth (" fifth ") rudimentary metatarsal ; the ra- 

 dius and ulna in the fore limb, and the tibia and fibula in the hind, 

 were distinct and well developed. The type so distinguished has 

 been named Eohippus by Marsh, and two sjDecies have been recog- 

 nized: it belonged, apparently, to the family of OroMppidoi., and prob- 

 ably was the nearest relative to the progenitors from which have 

 descended the modern equine mammals. 



Contemporary with these, and identifying their geological horizon, 

 was an animal whose remains have been identified both by Marsh 

 and Cope with the genus Coryplwdon^ long known by imperfect 

 fragments from the Lower Eocene beds of Europe. The more per- 

 fect remains found in this country prove that the animal was a gen- 

 eralized perissodactyle ungulate of peculiar fiimily, with five digits, 

 and not at all nearly related to the living Tapirids or the allied 

 Lophiodontids, as has been generally supposed. 



The mammals of the Eocene are the earliest of the higher types 

 of the class that have yet been discovered: between them and those 

 of the Trias a great blank intervenes, representing an enormous period, 

 and deposits of vast thickness, which have yielded up to the pres- 

 ent time no certainly identified remains of mammals, although, of 

 course, they must have been living during the whole of tliat epoch. 

 The conditions of life were very favorable, however, for the develop- 



