Prof. 0. C. Marsh — Hew Jurassic Dinosaurs. 257 



of vertebras, are inadequate, since they relate to one end only, tlie 

 other being supposed to correspond in form. The terms convexo- 

 concaA'^e, concavo-convex, plano-concave, etc., would be more accu- 

 rate, and equally euphonious. 



Fig. 4. 



Axis vertebra of Ceratosaunis nasicornis. 



Tn Ceratosaunis, as in all the Theropoda, except Cceliirus, the 

 cervical ribs are articulated to the centra, not coossified with them, 

 as in the Sauropoda. The latter order stands almost alone among 

 Dinosaurs in this respect, as both the Stegosauria and the Ornithopoda 

 have free ribs in the cervical region. 



The dorsal and lumbar vertebra are bi-concave, with only moderate 

 concavities. The sides and lower surface of tlie centra are deeply 

 excavated, except at the ends. These vertebras show the diplo- 

 sphenal articulation seen in Megalosaurus, and also in Creosaurus. 



All the pre-sacral vertebra are very hollow, and this is also true 

 of the anterior caudals. 



There are five well-coossified vertebrae in the sacrum in the pre- 

 sent specimen of Geratosaurus nasicornis. The transverse processes 

 are very short, each supported by two vertebrse, and they do not 

 meet at their distal ends. 



In the type specimen of Creosaurus, there are only two sacral 

 vertebrse coossified. In the Megalosaurus, there are five, and the 

 number appears to vary in difi"erent genera of the Theropoda, as it 

 does in the Sauropoda. 



The caudal vertebra ai-e bi-concave. All the anterior caudals, 

 except the first, supported very long chevrons, indicating a high, 

 thin tail, well adapted to swimming. The tail was quite long, and 

 the distal caudals were very short. 



The Fore Limbs. — The fore limbs in Allosaurus, and in fact in all 

 known Theropoda, were very small. The scapula and coi'acoid 

 resembled those of Megalosaurus. The humerus was short, and 

 somewhat sigmoid in form. The shaft was hollow, as in all the 

 limb bones of this genus. The manus was peculiar in having some 

 of its digits armed with powerful compressive claws, which formed 

 most effective weapons. These claws, in some allied forms, have 

 been referred to the hind feet, but the latter, in all the known 

 Theropoda, have their claws round, and not compressed. The fore 

 limb of Allosaurus fragilis is shown in Fig. 8. 



The Pelvic Arch. — The pelvic bones in the Theropoda have 

 been more generally misunderstood than any other portion of the 

 skeleton in Dinosaurs. The ilia, long considered coracoids, have 

 been since usually reversed in position ; the ischia have been regarded 



PECADE III. — VOL. I. — NO. VI. 17 



