90 THE CERATOPSIA 



Styracosaurus ovatus Gilmore 24 



Hnlotype: No. 11,869 U.S.N.M.; posterior portion of the crest and numerous detached fragments. 



Horizon: Two Medicine formation. 



Locality: Milk River, Blackfeet Indian Reservation, Glacier County, Montana. 



Collector: G. F. Sternberg, 1928. 



This species conforms to the generic characters in so far as determinable from the extremely 

 meagre type, which consists of the posterior part of the crest bearing the four median processes 

 together with a detached fragment bearing another. 



The original description follows: "The outstanding peculiarity of the skull of Styracosaurus 

 albert ensis is the large horn-like processes that project outward and backward from the posterior 

 border of the frill. Somewhat similar processes are present on the frill before me. The two processes 

 forming the hindermost pair lack their tips but it is quite evident they were not as long as in the 

 Canadian specimen. . . . Furthermore, these two horns are convergent as opposed to the divergent 

 processes in S. albertensis. It would seem that if completely preserved the extremities of these two 

 horns would nearly meet on the median line. Those of the next pair in advance are nearly as large 

 as the hinder pair but point outward more than backward. That there was a third pair is shown by 

 the presence of a small lateral section of the frill, from the side of which a small, stubby process 

 projects outward. ... If, as is apparent, this fragmentary part represents the third pair, these 

 processes have their origin considerably forward of the second pair as shown by the smooth, rounded 

 border between them. In S. albertensis these processes are relatively shorter, curved, and twinned 

 with the second pair at the base. 



". . . That large fontanelles were present on either side of a median bar as in S. albertensis is 

 shown by the rapid thinning of the bone on the anterior borders on either side of the middle, and 

 also of the posterior portion of the bar which is preserved. This part of the median bar is broadly 

 rounded transversely on the upper side but flattened beneath. 



"The upper and lower surfaces of the frill parts are marked by the usual vascular grooves. 

 The horn-like processes are much flattened above and below and cross sections taken from almost 

 any part would be broadly ovate in cross section." 



Thus, the main distinctions of the present species from S. albertensis are: processes III are 

 closer at the base and converging instead of diverging toward their tip, and there is a wider separa- 

 tion of processes I and II at the base. In albertensis, the processes are in contact} in ovatus, a rounded- 

 edged margin of crest lies between them, flat and sometimes slightly hollowed on the under side. 

 The presence of vascular impressions on the crest of ovatus in contrast to the smooth surface in 

 albertensis may be a matter of individual age, the former being the older, although somewhat more 

 recent in geologic time. 



The type of Monoclonius sfhenocerus Cope, from the Judith River of Montana, which consists 

 of the nasal horn, nasals, and part of the left premaxillary, is quite suggestive of the corresponding 

 part of S. albertensis. Of these, Lambe says, 25 "In Cope's species the nasal horn-core is farther 

 forward on the nasals, is proportionately shorter, and more laterally compressed, with a much 

 greater antero-posterior diameter at the base. The nasals in front of the horn descend rapidly 

 instead of rising conspicuously before they curve downward, and the nasal opening is larger and 

 placed more under the horn." 



As a matter of fact, the type of Monoclonius (Centrosaurus) nasicornus Brown is even more like 

 Styracosaurus in this particular portion than is that of M. sfhenocerus. The nasals in front of the 

 horn rise as in Styracosaurus, and agree in being highly rugose; the smaller nasal opening lies under 

 the anterior part of the horn, and the character of the horn itself agrees except for minor differences 

 which may be due in part to the manner in which the distal half of the Styracosaurus horn is 



24 Gilmore, C. W., 1930, pp. 36-37, PI. 10, Figs. 1, 2. 



25 Lambe, L. M., 1913, p. 115. 



