or horned Dirwsaurs, of Worth America. 177 



EXPLANATION OF PLATES. 



Plate I. 



Figure 1. — Skull of Triceratops ftabellatus. Marsh; seen from the left side. 



a, nasal opening ; b, orbit ; c, supra-temporal fossa ; e, epoccipital ; 

 h, horn-core; h'. nasal horn-core; p, pre-dentary; q, quadrate; 

 r, rostral bone. 

 Figure 2. — The same skull ; seen from behind. 



d, dentary ; p, parietal ; pel, pre-dentary ; s, squamosal. 

 Figure 3. — Skull of Triceratops serratus, Marsh ; diagram ; seen from above. 



d, epijugal bone; /, frontal; fp, postfrontal; /, jugal; m, maxiUary; 

 n, nasal; pf, prefrontal; pm, premaxillary; x, pineal foramen. 

 Figure 4. — Skull of Triceratops prorsus, Marsh ; seen from the front. 

 All the figures are one-twentieth natural size. 



Pla.te.IL 



Figure 1. — Anterior part of skull of Triceratops prorsus, Marsh; side view; one- 

 eighth natural size. 



Figure 2. — Front view of same. 



Figure 3. — The same ; seen from below. 



IV, nasal horn-core; n, nasal; na, narial aperture; pm, premaxillary ; 

 r, rostral bone. 



Figure 4. — Pre-dentary of same individual ; side view ; one-eighth natural size. 



Figure 5. — Top view of same specimen. 



Figure 6. — Bottom view. 



a, anterior end; b, upper border; d, groove for dentary; s, symphysis. 



Figure 7. — Cast of brain-cavity of Triceratops serratus, Marsh; side view; one- 

 half natural size. 

 c, cerebral hemispheres; cb, cerebellum; m, medulla; ol, olfactory 

 lobe ; on. optic nerve ; p, pituitary body. 



Figure 8. — Maxillary tooth of Triceratops serratus ; outer view ; natural size. 



Figure 9. — The same tooth ; side view. 



Figure 10. — The same tooth ; inner view. 



Figure 1 1 . — The same tooth ; seen from below. 



Plate III. 



Figure 1. — Anterior cervical vertebras of Triceratops prorsus, Marsh; side view. 

 Figure 2. — Fourth cervical vertebra of same series ; back view. 



a, anterior face of atlas; d, diapophysis; n, neural canal; p, pos- 

 terior face of fourth vertebra: r, rib; 5, neural spine of axis; 

 s / , neural spine of third vertebra ; s", neural spine of fourth 

 vertebra; z', posterior zygapophy sis. 

 Figure 3. — Anterior dorsal vertebra of same species; side view. 

 Figure 4. — The same vertebra ; front view. 

 Figure 5. — Posterior dorsal vertebra of same species; side view. 

 Figure 6. — The same vertebra; front view. 



a, anterior face of centrum ; h, facet for head of rib ; p, posterior face 

 of centrum ; s, neural spine ; t, facet for tubercle of rib ; z, anterior 

 zygapophysis. 



All the figures are one-eighth natural size. 



Plate IV. 



Figure 1.-— Sacrum of Triceratops prorsus. Marsh; seen from below; one-eighth 

 natural size. 

 a, anterior face of first sacral vertebra ; p, posterior face of last sacral 

 vertebra; s, neural spine of last vertebra; z, anterior zygapophysis 

 of first vertebra; 1-10, transverse processes, left side. 



