Condylarthra and Toxodontia. 



27 



"were probably 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 bone of the 

 lower jaw. 



One remarkable feature of this sub-order of Eocene mam- 

 mals is the diminutive size of the brain. It is, in fact, propor- 

 tionally smaller than in any other known mammal, recent or 

 fossil, and even less than in some reptiles. A cast of the brain- 

 cavity of Dinoceras is placed beside the reproduction of the skull. 



Casts of the skulls and bones of the Dinocerata, presented 

 by Professor O. C. Marsh, are exhibited in the Pier- case on the 

 South side of this Gallery, and a papier mache model of the 

 entire skeleton of Dinoceras mirahile (Marsh), is placed in a 

 glazed case in the centre of the Gallery, so that we can now 

 form, from their study, a very fair idea of this singular group 

 of huge Eocene herbivores, once so abundant in western North 

 America, to which region it appears to have been limited. 



Dinoceras. 



Pier-case, 

 No. 20. 



Pier-case, 

 No. 20. 

 South-side. 



See Glazed- 

 case, M.M., 

 in centre of 

 Gallery. 



Sub-order 5. — Condylarthra. 



This sub-order is only represented in the collection by Pier-cases 



portions of jaws with teeth of two genera, viz., Periptychus 

 and Haploconus from the Eocene of New Mexico, North America ; 

 and by an excellent coloured reproduction of the skeleton of 

 Phenacodus primcevus (Cope), from the Eocene of Wyoming 

 Territory, U.S.A. (see p. 28). 



Nos. 20 and 

 9. 



Sub-order 6. — Toxodontia. 



Under this sub-order are placed some large extinct Mammals Toxodon. 

 found in the Newer Tertiary deposits of South America, whose Pier-case, 

 exact zoological position is still rather uncertain. No * 20# 



Here are arranged incisor-teeth, also the skull and lower 

 jaw and some limb-bones of an animal named Toxodon, pro- 

 bably larger than a horse, but having Rodent-like incisor- 

 teeth in its jaws (the name being founded on the bow-like form 

 of these teeth). The remains of this remarkable animal were 

 obtained from the Pleistocene deposits ("Pampas-formation") 

 of Buenos Ayres. 



A plaster cast of an allied form Toxodontotherium is also 

 shown. 



From the same deposits was also obtained a large portion of 

 the skeleton of another aberrant form, related to the above, 

 but belonging to a much smaller animal, named Typotherium. 



