86 



Table-case, 

 No. 14a. 



Marsupialia — Microlestes, etc. 



from their teeth, so that their systematic position is at best 

 uncertain. 



To these discoveries must now be added a series of Upper 

 Jurassic mammalia from the " Atlantosaurus Beds," Wyoming 

 Territory, United States ; and of Cretaceous mammals from the 

 Laramie formation, Dakota and Wyoming, North America, both 

 discovered by Prof. 0. C. Marsh, and in many cases closely 

 related, if not identical, with genera previously known and 

 described from this country. 



With the exception of those placed in the Polyprotodont 

 division of the Marsupialia (see p. 76), these small mammals are 

 all provisionally arranged in the group of Multituberculata. 

 In the Tritylodontidee the upper true molars (of which there 

 are four) are ridged longitudinally. 



■^y>~ 



Fio. 109. — Lower Jaw and Teeth of Plagiaulax Becldesi (Falconer), twice natural size, 

 Middle Furbeck Beds, Dorset. 



Of the Bolodontidce several species have been found in the 

 Purbeck of England and Upper Jurassic of N. America, and 

 recently an incisor apparently of a species of Bolodon has beeu 

 discovered in the Wealden of Sussex. 



In the Plagiaulacidce the premolars in the mandible vary in 

 number from one to four, have a cutting edge, and are marked 

 by a series of oblique lateral grooves, while the true molars are 

 small, and usually reduced to two in number. Probably they 

 all had two lower incisors and two functional upper ones. 



Fig. 110. — Upper true molar of Neoplagiaultir eocenus (Lemoine). Lower Eocene, 

 Kheims, France. 



Plagiaulax occurs in the Puidoeck Beds of Swanage and 

 probably in the Wealden of Hastings. It is represented by 

 Ctenacodon in the U. Jurassic and by Halodon in the Cretaceous 

 of Wyoming, by P Modus from the Puerco Eocene of New 

 Mexico, North America ; and by Neoplagiaulax from the Lower 

 Eocene of Rheims. 



