[903.] Lull, Skull of Tficcratops Serratus. 693 



tals and to a less extent into the squamosals, thus implying a 

 compactly fitting integument. The base, especially of the 

 right horn core, is well preserved. It is extremely hollow, but 

 with a shelf-like circular projection of bone running around the 

 inner wall just above the level of the postfrontal bones with- 

 out, and doubtless to aid in resisting the thrust of the latter 

 bones when lateral pressure was brought to bear upon the 

 horns. Around the outside base of the horn is a horizontal 

 ridge which may have supported the base of the horny sheath. 

 The orbits are nearly circular and are surrounded by a thick- 

 ened ridge of bone, especially in front. The downward and 

 outward crushing of the left horn core has partially closed the 

 left orbit, adding to the sinister expression of the skull. 



The Lower Jaw. 



The left 'mandible, which is admirably preserved, consists of 

 dentary, surangular, and coronoid, with a full magazine of 

 thirty -nine vertical rows of teeth. On the inner face is a row 

 of thirty-eight dental foramina, and the meckelian groove on 

 the inferior face is wide and deep, but was covered by the thin, 

 plate-like splenial which, though lying detached in the quarry, 

 presents a perfect contact when placed in position. Cope ^ 

 claims that in Hadrosaurus it is the splenial which contains the 

 magazine of teeth . Whether or not this be true of Hadrosaurus 

 it is certainly not true of Triceratops, in which the magazine is 

 contained in the dentary in the normal manner. The teeth 

 arise in alternate series in the successive vertical rows, only one 

 series being in full use at one time, though those of the 

 secondary series, arising between the teeth of the primary 

 series, show partial wear, while in the posterior part of the 

 jaw individual teeth of the primary set are already succeeded 

 by tertiary teeth. The vertical worn faces of the teeth present 

 the surface known to mathematicians as an hyperbolic para- 

 boloid or warped surface ; the whole mechanism reminding one 

 of a slightly twisted saw with alternating higher and lower teeth . 

 Marsh notes the fact that in the Ceratopsia the teeth are 

 double-rooted, a feature almost unique among reptiles. This 



' Cope, E. D., Amer. Naturalist, July, 1S83, p. 775 



