224 PIIOCEEDINGS OF THE NATIONAL MUSEUM vol.83 



Order Carnivora — Continued. 

 Arctoc3'onidae — Continued. 



Metachriacus provocator, new species. 



Spanoxyodon latrunculus, new genus and species. 



Tricentes latidens, new species (Gidley). 



Coriphagus monianus Douglass, 1908. 

 Miacidae: 



Ictidopappus vixistelinus, new genus and species. 



Didymictis tenuis, new species. 



Didymictis microlesies, new species. 



Didymictis haydenianus Cope, 1882. 

 Order Condylarthra: 

 Phenacodontidae: 



Tetraclaenodon symbolicus, new species (Gidley). 

 1 Tetraclaenodon superior, new species. 



Gidleyina montanensis, new genus (Simpson) and species (Gidley). 

 '^Gidleyina silberlingi, new species (Gidley). 

 Hyopsodontidae: 



Ellipsodon aquilonius, new species. 



Litaletes disjundus, new genus and species. 



Litomylus dissentaneus, new genus and species. 



Haplalctes disceptatrix, new genus and species. 

 Order Amblypoda: 

 Pantolambdidae: 



Pantolambda intermedins, new species. 



Paniolambda cf. cavirictus Cope, 1883. 

 Periptychidae: 



Anisonchus sectorius (Cope, 1881). 

 Incertae sedis: 



Picrodus silberlingi Douglass, 1908. 



Megopterna minuta Douglass, 1908. 



Order MULTITUBERCULATA 



Family PTILODONTIDAE 



Ptilodontids are very abundant and surprisingly varied in the col- 

 lection. After prolonged analysis, which cannot be published here, 

 eight sharply distinct species are definable and at least one other is 

 represented by fragmentary specimens. Although the species are 

 readily distinguishable from one another and from all others known, 

 their generic assignment is uncertain in every case but one. There 

 are five named genera of ptilodontids in the American Paleoconc, and 

 some of these species almost certainly belong to new genera, but these 

 cannot now be defined. It is usually impossible to be sure of a generic 

 assignment without associated incisors, last lower premolars, and last 

 upper premolars, which are not available for seven of the eight species 

 in the collection. Generic assignments are thus made with a query 

 on an insecure basis of general resemblance, and the delinilions dis- 

 tinguish the species from all known ptilodontids and not merely from 

 those of the genus to which each is referred. Far the most abundant 



