LEPTOCERATOPS GRACILIS 81 



dinosaurs in the possession of extremely long spines, especially in that area of the tail which lies 

 behind the greatly elongated ischia, as though each possessed a flattened, crested tail almost that of 

 a modern basilisk. See, however, Knight's restoration of Protoceratops in the frontispiece. 



The ilia are alike, and differ from those of other ceratopsians in that they lack the reflected 

 upper border which, in the latter, overhangs the acetabulum, making the blade of the ilium nearly 

 horizontal instead of vertical. The ischia, long and straight, and the very peculiar pubes ( Figs. 36, 

 37), with relatively short prepubes, are also in agreement with each other to the exclusion of other 

 forms. Comparable also are the femora, with a large fourth trochanter, and a well-defined third 

 trochanter. In each, the unguals are slender and compressed, more like those of Camftosaurus 

 than of a more typical ceratopsian. 



These many details of agreement point to a very close relationship on the part of the two 

 genera and a wide divergence from all other known members of the superfamily Ceratopsoidea. I see 

 no indication of ancestry on the part of Protoceratops; certainly Leptoceratops of the Edmonton, 

 which is later in time than all of the Belly River, Judith River, and Two Medicine genera, and con- 

 temporaneous with Anchiceratops and Arrhinoceratops, is debarred by time from actual ancestry of 

 any of them, and its characters are not such as would permit it to be even a structural ancestor of any 

 of the Lance forms. 



Protoceratops and Leptoceratops, each with its single known species, belong to the same family 

 Protoceratopsidae proposed by Granger and Gregory, but denned by Gregory and Mook. 7 The 

 family characters lie in those details which both genera show in contrast to the Ceratopsidae, and 

 include hornlessness, premaxillary teeth, single-rooted maxillary and mandibular teeth, and the 

 peculiarities of ilia, pubes, and caudals which I have stressed. 



Family CERATOPSIDAE Marsh 



The characters of the family may be stated as follows: large; highly specialized ; skull bearing 

 horns; with secondary roofing above the frontals; crest generally with epoccipital bones; without 

 premaxillary teeth; cheek teeth with bifid roots; fore limb shorter than hind; blade of ilium 

 horizontal; prepubic process comparatively large and expanded vertically at the anterior end; fourth 

 trochanter of femur nearly obsolete, femur longer than tibia; unguals of manus and pes depressed 

 and hoof-like; midcaudal vertebral spines not elongated. 



Genus MONOCLONIUS Cope (Judith River phase) 



The type species of the genus Monoclonius is M. crassus, described by Cope in 1876, from the 

 Judith River beds of Montana. Three other species were described later in 1889. They were 

 M . fissus, M. recurvicornis, and M. sphenocerus. Because of the fragmentary character of the type 

 material, the doubt of actual association of the various elements in single individuals or even species, 

 and the fact that homologous parts of the different types are rarely preserved, it is extremely difficult 

 to define the genus in detail, and next to impossible to compare all the species. The same is true 

 of the species of Ceratops, as described by Marsh, which come from the same general horizon and 

 locality. 



The several species from the Belly River formation which have been described by Brown as 

 Monoclonius belong to the genus originally described by Lambe as Centrosaurus, with the species 

 apertus as the type. If the generic identity of Centrosaurus and Monoclonius is finally determined 

 without question, the latter takes precedence. On the basis of present evidence, I am inclined to 

 consider Centrosaurus a local, Belly River phase of Monoclonius., possibly of sub-generic rank. 



In the morphological chapter of this memoir the skeleton of Monoclonius {Centrosaurus) flexus 



"Granger, W., and Gregory, W. K., 1923, p. 4. 

 7 Gregory, W. K., and Mook, C. C, 1925, p. 4. 



