126 THE CERATOPSIA. 



so as to form a complete covering and efficient armor for the short cervical region restricted in 

 the Ceratopsia, as in most Mammalia, to the seven [eight, R. S. L.] anterior presacral vertebrae. 

 The periphery of this frill bore seventeen triangular epoccipital bones. The broader of these 

 occupied a median position relative to the parietals, while the remaining sixteen were arranged in 

 pairs, eight on either side, diminishing in size as they recede from the median. The third of 

 these laterally paired epoccipitals is supported about equally by the parietals and squamosals, 

 while the first two pairs are borne by the parietals and the five remaining pairs are borne by 

 the squamosals. ' The last two pairs of the latter five, instead of being borne on the extreme 

 margin of the frill as are the others, are shifted to the superior surface of the squamosals and 

 are much smaller than those located between them and the single median ossicle. The number 

 of these epoccipital bones appears to vary from seven lateral on either side and one median, 

 or fifteen in all, in the type of Triceratops prorsus as figured by Marsh, to nine lateral and one 

 median, or nineteen in all in the type of Sterrholophus fldbellatus as figured b}^ that author. 

 The number of epoccipitals may, however, have varied in different individuals and can hardly 

 be considered as diagnostic of the different genera or species. 



The lower jaw was proportionately long and slender and the predentary seems to have 

 been somewhat elongated, though the anterior portion is wanting. There is 'a marked protuber- 

 ance near the middle of the inferior border, and above this are a number of foramina, the three 

 larger of which are arranged in a series one behind the other and in the same horizontal plane. 

 The coronoid process is strong and moderately expanded above. As nearly as can be deter- 

 mined the articular, angular, and surangular do not differ materially from the same elements 

 in Triceratops prorsus. 



Seen from the side with the lower jaws in place, as they were found, the skull appears long, 

 broad, and low. The superior surface between the midfrontal region and the median epoccipital 

 is deeply concave antero-posteriorly, much more so than is shown in PI. XXVII. The superior 

 surface of the nasals, prefrontals, and frontals is slightly concave. The orbits are large and 

 irregularly elliptical in outline, not "nearly circular" as originally described by Marsh. The 

 hard sandstone matrix in which the skull when found was embedded has not yet been removed 

 from the under surface, so that I am unable to describe the palatal view. 



The characters which at present seem most distinctive of this species are (1) the position 

 of the lachrymal foramen, which lies between the maxillary and nasal instead of within the 

 maxillary; (2) the structure of the inferior temporal arch; (3) the comparatively slender supra- 

 orbital horn cores; (4) the narrow and elongated lateral temporal foramen. The number of epoc- 

 cipitals and the rugosities mentioned by Marsh as present on the squamosals may also prove 

 to be of specific importance. 



Principal measurements of type of T . serratus (No. 1823, Yale Museum). 



Mm. 



Greatest length of skull : 1, 710 



Greatest breadth of frill 1, 150 



Expanse of jugals — 630 



Expanse of frontal region at anterior border of orbits. . 369 



Greatest diameter of orbit 136 



Least diameter of orbit 110 



Greatest diameter of lateral temporal fossa. 108 



Least diameter of lateral temporal fossa 45 



Distance from posterior border of orbit to posterior border of frill : 828 



Thickness of postfrontal behind orbit 159 



Antero-posterior diameter of supraorbital horn core immediately above orbit . 173 



Antero-posterior diameter of supraorbital horn core 200 mm. above orbit 115 



Transverse diameter of supraorbital horn core immediately above orbit 132 



Transverse diameter of supraorbital horn core 200 mm. above orbit 95 



Greatest length of squamosal 785 



Greatest breadth of squamosal 400 



Length of parietals along median line 652 



Distance between squamosal sutures at posterior border of frill ' 900 



Distance between squamosal sutures at junction with postfrontals 297 



