X ORTHOPODA — STEGOSAURI 425 



ous, and frequently long, especially on the anterior half of the 

 long and heavy tail. 



Orthopoda occur from the Lias to the Upper Cretaceous, 

 both in Europe and in North America. The name Orthopoda, 

 invented by Cope in 1866, is appropriate for obvious reasons ; 

 it comprises the Stegosauri and Ornithopoda of Marsh (1881). 

 The latter term is not very fortunately chosen, considering that 

 the whole hind-limb of the Theropodous Com^Jsognathus is far 

 more ornithic than that of any three-toed Ornithopoda, in which 

 the tarsalia rarely fuse with the tibia and never with the meta- 

 tarsals. To apply the term Ornithopoda to the whole order is 

 quite unjustifiable, unless it is meant to apply to the strikingly 

 bird-like configuration of the pelvis. 



Sub-Order 1. Stegosauri. — The fore- and hind-feet are planti- 

 grade, or nearly so, the metapodials being but little elongated, 

 with more than three functional digits. The bones of the limbs 

 are solid. The ribs of the trunk are bifurcated, and are carried 

 by the diapophyses of the neural arches. The body, especially 

 the back, is protected by dermal bony plates, which are not con- 

 nected with the internal skeleton. 



Scelidosaurus harrisoni. One nearly complete skeleton, about 

 1 1 feet in length, from the Lias of Lyme Regis. About twenty- 

 four pre-sacral vertebrae, of which six or seven belong to the neck, 

 four sacral and about forty caudal vertebrae. Four fingers, four 

 toes, with 2, 3, 4, 5 phalanges, the fifth metapodials being quite 

 vestigial ; the hallux and poUex are very short, so that the foot 

 at least is functionally tridactyle. The tarsal bones remain 

 separate. The head is very small. Two rows of ridged bony 

 plates extend from the neck over the back, and converge into one 

 row upon the long tail ; smaller plates, arranged in many rows, 

 seem to have protected the sides and under parts. Hylaeosaiorus 

 and Polacanthus of the English Wealden are allied forms. 



Stegosaurus, with several species from the Upper Jurassic of 

 Colorado and Wyoming, and others, e.g. S. armatus ( = Omosaurus), 

 from the Kimmeridge Clay of Wiltshire in England. The head 

 is relatively very small, and the brain is surpassed several times 

 in thickness by the huge sacral swelling of the spinal cord. 

 Teeth numerous and small. All the cervical and trunk-vertebrae 

 carry bifurcated ribs, those of the trunk being carried entirely by 

 the very high neural arches. The fore-linjbs are only about half 



