lo AMERICAN MESOZOIC MAMMALIA 



Cope included three families in his suborder : Tritylodontidae, Polymastodonti- 

 dae, and Plagiaulacidae. In 1887 he added the Chirogidae, based on the genus Chirox 

 and supposedly intermediate between the Plagiaulacidae and Polymastodontidae. 



Osborn's classification of 1888 (i888a) maybe summed up as follows: 



[Order Marsupialia] 



Suborder Multituberculata 

 Plagiaulacidae 



Microlestes, Ctenacodon, Plagiaulax, Ptilodus, N eofl agiaulax, 

 Meniscoessus, "and perhaps also Thylacoleo." 

 Bolodontidae 



Bolodon, Allodon, and possibly Chirox. 

 Tritylodontidae 



Tritylodon, Triglyfhus. 

 Polymastodontidae 

 Polymastodon 

 Incertae sedis: Stereognathus. 



In 1889 Marsh proposed several new families for Lance (upper Cretaceous) gen- 

 era: Cimolodontidae, Dipriodontidae, Tripriodontidae, Cimolomidae. He also stated 

 that one form belonged to "the family named by the writer, the Allodontidae." The 

 latter family had not, however, been previously mentioned. It was apparently ad- 

 vanced on grounds similar to those for the Chirogidae and Bolodontidae, with which 

 it was probably meant to be synonymous. In 1887 Marsh had definitely stated that 

 Allodon belonged to the Plagiaulacidae, and the retreat implied in 1889 was, as time 

 has shown, an unfortunate step away from the true expression of relationships. 



In his first review of Marsh's work, Osborn placed the Cimolomidae and Cimolo- 

 dontidae in the Plagiaulacidae. He also erected the family Stereognathidae "dis- 

 tinguished by the presence of two rows of tubercles in the upper molars and three in the 

 lower, of the crescentoid pattern" to include the Dipriodontidae and Tripriodontidae, 

 as well as Stereognathus itself. In his later work on Lance mammals, however (1894), 

 Osborn abandoned this modification of his familial classification, recognizing its 

 erroneous basis and referring all upper Cretaceous multituberculates to the family 

 Plagiaulacidae. 



In their joint paper on the mammals of the Puerco (1895) Osborn and Earle 

 proposed dividing the Plagiaulacidae into the two subfamilies Plagiaulacinae and 

 Polymastodontinae, which they defined. 



Finally, in 1909, Gidley showed that Chirox was based on the upper jaw of 

 Ptilodus. Although he did not redefine the families, it obviously followed that the 

 families Chirogidae, Allodontidae, and Bolodontidae were invalid. 



By the steps now very briefly recapitulated, there has been achieved a twofold or 

 threefold division of the order. Typical of recent views is that given by Schlosser in 

 the 1923 edition of the Zittel Grundzilge: 



