STEKRHOLOPHUS FLABELLATUS. 145 



CHARACTERS OF SKULL. 



The squamosals (Pis. XLIV, XLV, and figs. 6, 10, 11, 15). — These are rather broad and short 

 for one of the larger members of the Ceratopsia. As pointed out by Marsh, both the superior 

 and inferior surfaces of these bones, as well as the parietals, are smooth and entirely destitute of 

 those rugosities and channels present on these elements in other skulls of the Ceratopsia. Marsh 

 has considered this character in the present specimen as alone of generic importance, but to 

 the present writer it appears to be more probably due to the immature age of the individual, 

 while it is quite conceivable that sex may also have had something to do with it. The external 

 border of the squamosal describes the arc of a rather large circle. The parietal border is very 

 thick and concave fore and aft. Behind the buttress for the exoccipital process the squamosal 

 sends forward and upward a broad thin plate for articulation with the postfrontal and jugal, 

 while the lowermost of the three anterior processes shown in fig. 10 overlaps the quadrate and 

 to a small extent the quadratojugal. The antero-inferior border of the squamosal falls far 

 below the quadrate and forms the posterior border of the quadratojugal notch. The antero- 

 inferior angle describes the arc of a rather small circle, and its inferior surface is strongly convex, 

 while the superior is concave. The inferior surface is broadly concave anteriorly. 



The parietals (figs. 10 and 11). — Only the left parietal and a very small portion of the 

 anterior part of the right is preserved and since no very distinct suture is shown between these 

 elements, notwithstanding the immature age of the specimen, it would appear that the parietals, 

 if ever distinct, must have become completely fused very early in life. On account, however, 

 of the fractured condition of the bone in the region where the suture should appear if actually 

 present, it is not possible to determine definitely whether or not there be a suture. The parietals 

 are proportionally broad behind and narrow in front, but aside from the absence of rugosities 

 and that system of grooves and channels on the surfaces of the bone, already referred to, they 

 do not differ materially from those elements in the genus Triceratops. 



The postfrontals (Pis. XLIV, XLV, XLVI, figs. 6, 10, 11).— The postfrontals are, as usual 

 in the Ceratopsia, the most massive elements in this region of the skull. In PI. XLIV, prepared 

 under the direction of Professor Marsh, they are figured as extending a little too far backward 

 and as being destitute of a postfrontal (pineal) foramen. A careful examination of the specimen 

 shows this foramen to have been present, the left lateral border of it still being preserved. 

 Posteriorly the postfrontals are in contact with the parietals and squamosals, laterally with the 

 squamosals and jugals, medially they oppose one another, anteriorly they appear on the external 

 surface of the skull as articulating with the frontals and prefrontals, while below they send 

 forward a long wedge-shaped mass which passes beneath the frontals and overlaps the alisphe- 

 noids, forming a small portion of the roof of the exit for the olfactory nerve, as shown in fig. 9. 



Below, the postfrontals are supported from behind by the supraoccipitals, parietals, and 

 squamosals, and in front by the alisphenoids. Posteriorly they are invaded by a number of 

 large chambers which are more or less completely connected with one another and with the 

 very large cavities at the bases of the horn cores. Some of these chambers connect with the 

 postfrontal (pineal) foramen, and perhaps also with the supratemporal foramina. The post- 

 frontals form the posterior one-half of the orbital borders and give origin to the powerful supra- 

 orbital horn cores, which in the present specimen are rather long and slender, nearly circular 

 in cross section distally and ovate proximally where the fore-and-aft diameter is the longer and 

 the posterior surface describes the broader end of the figure. 



As it lay embedded in the sandy matrix the left horn core, which was the only one of the 

 two preserved, was incased in a soft, light-colored, decomposed mass of fibrous material about 

 one-quarter of an inch thick, which doubtless represented the disintegrated horny sheath with 

 which in life the horn core was covered. 



The frontals were small and closely applied to each other. They are somewhat injured and 

 it is not possible to determine with accuracy their true form. They are seen, however, to have 

 overlapped the postfrontals behind and the nasals in front. 



MON XL1X — 07 10 



