196 Bulletin American Museum of Natural History. [Vol. XXVII, 



A. (AviphitTjlus) owcni. The coronoid was broad as in the Polyprotodont 

 Marsupials. 



The Amblotheriidse, Stylacodontidae, Kurtodontidse and Dicrocyno- 

 dontidae, formerly brought together by Osborn as the suborder Insectivora 

 Primitiva (1888, p. 247) but later grouped by him (in Zittel's Palseontologie) 

 with the Amphitheriidse as the order Trituberculata, present so many 

 analogies in the dentition and mandible to the Insectivora that if experience 

 had not taught us to distrust the dentition as a guide to Interordinal affinities, 

 no hesitation would be felt in placing all these families except the Dicrocyno- 

 dontidoe in the Placental order Insectivora. Some of the features occurring 

 among both the Trituberculata and the Insectivora include the following: 



(1) Incisor series prolonged backward on the side of the mandible. 



(2) Canine either erect, recurved, or more or less premolariform, with 

 two roots. 



(3) Cheek teeth with prong-like, more or less recurved cusps. 



(4) Lower molars short antero-posteriorly, with very small low talonid 

 and high trigonid. 



(5) Upper molars very broad transversely, narrow antero-posteriorly 

 (Kurtodon, Dryolestes. Compare Microgale, Ericulus). 



(6) Condyle sometimes set low, near level of cheek teeth. 



(7) Coronoid varying from broadly triangular {cf. Centetes) to delicate, 

 recurved {cf. Tupaia). 



(8) Two mental foramina (Leptocladus), beneath pj and m^, respectively. 

 In case the affinity of the Trituberculata to the Insectivora should ever 



be proven certain characters may be discovered that would warrant placing 

 the Trituberculata in the jNIonodelphia (Placentalia). But in view of the 

 characters shared by Amphitherium with certain Triconodonts and Poly- 

 protodonts on the one hand and with the "Insectivora Primitiva" on the 

 other it does not seem advisable at present to separate the Triconodonta and 

 Trituberculata by placing the former in the Marsupialia, the latter in the 

 Monodelphia; accordingly, in the classification adopted below (p. 464) 

 the Trituberculata are placed in the infraclass Metatheria, the earliest 

 representatives of ^\■hich are usually regarded as ancestral to both Marsu- 

 pials and PJacentals. 



On account of the very limited material it is difficult to find any characters 

 for diagnostic purposes that apply to all members of the TritubercvUata. 



The group is separated from the Polyprotodont Marsupials by the 

 retention of four premolars (five ? in Aviphitherium) and usually by the higher 

 number of molars and incompletely inflected angle. From the Placentals 

 the group is separated frequently by the higher number of incisors (|) and 

 molars (usually 6-8, but in Paurodon 3 ?). 



