[lambe] crest of the HORNED DINOSAUR CENTROSAURUS 5 



circular, whilst in the corresponding position on the other side 

 it is decidedly thickened next to the fontanelle. Elsewhere the 

 bone forming the margins of the fontanelles is thin, and 

 comes gradually to a sharp edge. The right outer side of the crest is 

 regularly scalloped from near the hooked process forward to a point 

 almost in line with the front end of the fontanelle, from which point 

 the squamosal suture extends forward and inward for some distance, 

 as indicated in figures 1 and 2, and in the text figure, at a. The five 

 protruding portions of the outer undulating margin bear sharp-edged 

 epoccipital bones, with the exception, apparently, of the anterior one, 

 which was partially in contact with the squamosal. The epoccipitals 

 decrease in size forward and appear to have been firmly coossified with 

 the underlying bone, the foremost one of the four, however, still showing 

 the line of junction clearly. They lie in the general plane of the alar 

 extensions, with their greatest diameter in an antero-posterior direction. 

 Between them the bone is regularly emarginated and is evenly rounded 

 at the edge. The coossification of the epoccipitals with the bone beneath 

 would indicate an animal of mature age. The hooked processes appear 

 to be a special development of the epoccipital bones and are of so extra- 

 ordinary a nature as to demand special attention. xA.nteriorly the post- 

 frontal suture, h, figures 1 and 2, and text figure, extends forward from 

 the inner side of the front end of the fontanelle, in a general direction 

 parallel to that of the squamosal, round the front end of the elevated 

 axial ridge to meet the suture from the other side in the median line. 

 The coalesced parietals extended beneath the postfrontals and squamo- 

 sals as is indicated by the smoothness of the upper surface of the bone 

 and its increased thinness in front of the groove or step marking the 

 back limit of the suturai contact. At the extreme anterior end of the 

 crest two vertical flanges of bone, one on each side of the median line, 

 separate a deep central depression from lateral ones of about eqiial 

 depth and size. Behind these latter occur smaller but deep pits that 

 run beneath the edges of the elevated median ridge : these two pits are 

 cut off from the more anterior pair by stout Inittresses of bone. These 

 five depressions evidently provided an increased surface of contact 

 between the parietals and the postfrontals, where the principal strain 

 in the support of the crest probably came and where great strength with 

 lightness was no doubt requisite. On the lower surface the axial portion 

 for a short distance in advance of the transverse posterior l)ar is flat, 

 but in front of this the bone, on account of its increasing thinness as 

 the front of the crest is approached, conforms more nearly with the 

 general form of the upper surface so as to be deeply hollowed out in a 

 longitudinal direction below. The lower surface of the crest is smoother 



