MAMMALIA. 83 



The largest of these mammals are represented in the Table-case 



Lower Eocene of New Mexico, U.S.A., by jaws which are 

 named Polymastodon in allusion to their "teeth with many 

 nipples." One piece of jaw and two plaster casts of com- 

 plete jaws are exhibited in Table-case 14a. A much smaller 

 Multituberculate, Ptilodus, occurs with Polymastodon in New 

 Mexico, while the allied JVeoplagiaulax (Fig. 78) is found in 

 the Lower Eocene of Eheims, France; but there are no 



14a. 



Pig. 78. — Upper molar tooth of Neoplagiaulax eocenus, grinding surface 

 and two lateral aspects, from the Lower Eocene of Rheims, France ; 

 the lower line indicating nat. size. (After Lemoine.) 



specimens of these in the collection. Nearly similar teeth 

 and jaws are met with in the Upper Cretaceous Laramie 

 Formation of North America ; and others, of the genus 

 Plagiaulax, of which several jaws are shown in the Beckles 

 Collection from the Purbeck Beds, have cutting teeth in 

 front and multituberculate teeth only behind (Fig. 79). 



Two-rooted multituberculate teeth, belonging to an un- 

 known animal named Microlestes, are found even in the 



Fig. 79. — Lower jaw and cutting teeth of Plagiaulax becklesi, from the 

 Purbeck Beds of Swanage ; twice nat. size. (Table-case 14a.) 



Ehsetic Formation of England and Wurtemberg. Specimens 

 of the very small M. moorei are exhibited from a Ehsetic 

 fissure- deposit at Holwell, near Frome. They bear tubercles 

 round the edge of the crown and closely resemble the binder 

 teeth of Plagiaulax. A skull with multituberculate teeth 

 from the Upper Triassic Karoo Formation of South Africa 

 was also placed here for some time. This (Fig. 81) was 

 described under the name of Tritylodon longsevus and 

 assigned to a mammal by Owen ; while a fore limb from the 

 same formation, named Thwiodesmus phylarchus by Seeley, 



G 2 



