150 The Ottawa Naturalist. [Dec. 



tion, may be said to consist of a longitudinal or axial part, a 

 transverse portion forming the posterior border, and lateral or 

 alar extensions that complete the sides and front margin. . . . 

 The posterior bar near the median line presents a backwardly 

 directed vertical face, which becomes rounded and less robust 

 in the neighbourhood of the hooked processes; it is not, however, 

 quite bilaterally symmetrical, its transverse section near the left 

 hooked process being nearly circular, whilst in the corresponding 

 position on the other side it is decidedly thickened next to the 

 fontanelle. ... A shallow groove, g, more clearly shewn 

 on the right side of the specimen, extends on the anterior side 

 of the posterior bar from the upper surface near the median line 

 downward and then upward in a regular curve, ending at a point 

 in advance of the base of the hooked process. Above this groove 

 the face of the bar presents a broken surface. On the left side 

 the corresponding groove is only faintly indicated, and the bone 

 above it is intact." It is this broken surface on the anterior 

 right margin of the posterior bar which is of special interest at 

 the present time. To this surface the lower broken base of the 

 "horn-core"fitsexactly in perfect contact. To Mr. Bamum Brown 

 of the American Museum of Natural History, New York, belongs 

 the credit of having made this discovery whilst on a visit to the 

 Geological Survey at Ottawa during the past summer. 



What w'as at first considered to be a nasal horn-core is thus 

 proved to be a strong, forwardly directed outgrowth or spur 

 from the anterior surface of the right lateral half of the posterior 

 bar passing directly across and over the right fontanelle, the 

 front end of the spur being about one inch only above the surface 

 of the bone forming the anterior border of the opening. Thus 

 the above-mentioned groove, g, passes beneath w^hat is now 

 known to be the base of the robust outgrowth. What is sur- 

 prising is, that there was no corresponding outgrow'th from the 

 posterior bar on the left, the surface of the bone there being quite 

 smooth, as already stated. 



The figure of the parietal crest accompanying this notice 

 shews the newly discovered outgrowth in its proper position 

 somewhat marring the symmetry of the specimen, but certainly 

 providing food for speculation as to its true nature. 



The hooked processes on the posterior margin of the crest 

 of Centrosaurus were probably of some use in a protective sense. 

 Projecting beyond the back of the frill, and with a horny cover- 

 ing, they would play an important part in the marginal armature 

 of the frill. The outgrow1;h over the fontanelle, however, as it 

 lay but little above the general plane of the lateral expansion of 

 the crest was probably enveloped by the covering of the frill 

 and did not shew to anv extent above its surface; to be of use 



