order vni DIXOSAUMA 241 



series. Dorsal vertebrae opisthocoelous ; caudals amphiplatyan. Other 

 characters as in Iguanodon. Upper Cretaceous j New Jersey, Dakota, and 

 Montana. 



Claosaurus, Marsh. Skull very similar -to the preceding, and the genus 

 possibly not distinct from Trachodon. Nostrils large, and no supra-orbital 

 bones observed. There are thirty presacral vertebrae, nine fused sacrals, and 

 about sixty caudals. All the presacrals are opisthocoelous and costiferous : 

 anterior caudals also opisthocoelous, and with very long chevron bones. Fore- 

 limbs unusually short and small in proportion to the hinder pair. In the 

 maims digit I is rudimentary, and Xo. V is wanting ; functional digits 

 hoofed, each with three phalanges. Functional digits of hind foot very 

 massive, with broad hoofs; their formula 0, 3, 4, 5, 0. C. annectans. Marsh, 

 attains a length of 9 m. A complete mounted skeleton in Yale Museum. 

 Upper Cretaceous ; Colorado, Wyoming, and Montana. 



IAmnosaurus, Nopsca. Cretaceous; Austria. 



Family 2. Stegosauridae. Marsh. (Scelidosauridaej Huxley.) l 



Skull small, without antorbital vacuity ; nostril* large and placed far forwards . 

 premaxillae edentulous. Vertebrae amphicoelous or amphiplatyan, and solid through- 

 out, like the limb bones. Post-pubic process robust ; fore-limbs much smaller titan the 

 hinder pair. Feet plantigrade, tri- or penta-dactyle, with short, hoof -like, ungual 

 phalanges. Exoskeleton strongly' developed, consisting of a series of large dermal 

 plates and spines. Lias to Upper Cretaceous. 



This family comprises moderate or large-sized Predentata, with well- 

 developed exoskeleton, solid limb bones, and solid amphicoelous or amphi- 

 platyan vertebrae. The dermal armour usually consists of large bony 

 plates or spines, but in a few genera the back is encased in a continuous 

 shield of fused plates (Polaeanthus). The neural canal of the sacrum is 

 sometimes enormously expanded. In the pelvis the post -pubic process is 

 greatly extended, as in the Ornithopodidae, and there is likewise a marked 

 disparity between the fore- and hind-limbs. The gait was probably in most 

 cases quadrupedal, although a study of femoral characteristics has led Dollo 

 to suggest that they may have been at least at one stage bipedal. 



Stegosaurus, Marsh (Figs. 346-348). Skull narrow and depressed, relatively 

 very small, and brain cavity in proportion to size of the body more diminutive 

 than in any other land vertebrate. Orbits small; laterally directed; supra- 

 temporal vacuities small and rounded ; nasals nearly half as long as the skull. 

 Mandibular ramus deep, pierced by a lateral foramen. Teeth very numerous, 

 bluntly pointed, more or less spatulate in form, loosely socketed in a single 

 functional series. Vertebrae slightly amphicoelous or with flat ends, the 

 cervicals with short ribs and dorsals with much elevated neural arches, on 

 which the stout dorsal ribs are borne. Sacrum of four fused vertebrae, some- 

 times with one or more lumbars added on in front : their neural canal enlarged 



1 Literatu iv : 



Bunzel, /•;.. Reptilien der Gosauformation (Abhandl. Geol. Reichs, Anstalt, voL V. pt. 1), 1871. 

 —Davies, W., On the exhumation of Oiuosaurus (Geol. Mag. [2J vol. III. p. 193), 1876.— Rulke, 



J. IT.. On Polaeanthus (Phil. Trans, vol. CLXXVI1I. B. p. 169), 1887.— Marsh, <>. C, On Scleido- 

 saurus, etc. (Amer. Journ. Sci. [3], vol. L.), 1895. — Sedey, II. G., The Reptile Fauna of the Gosau 

 Formation (Quar. Journ. Geol. Soc. vol. XXVI. p. 620). 1881.— On Polaeanthus, etc. [ibid. vol. 

 XLVIII. p. SI), 1892. 



VOL. II R 



