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FOSSIL REPTILIA OF THE 



This character is strongly marked in dorsal vertebras of the present genus, and with 

 modifications which could hardly have been illustrated or made clear without the above- 

 cited figures of the vertebras of previously defined Dinosaurian genera. In these, 

 however, the degree of complexity of the neural platform varies ; it is least marked in 

 the smaller and more crocodilioid genus Scelidosaurus (Pal. vol. for 1860, ' Liassic 

 Dinosauria,' pp. 5 — 7, Tabs. II — VI). 



The vertebra of Omosaums — the subject of Plates XII, fig. 1, and XIII — has come 

 from the middle of the trunk. This is inferred from the position of the surface, p, for 

 the head of the rib, which has risen from the centrum, or base of the neural arch, to near its 

 summit, where, with its diapophysial productions, a, d, the arch expands to a breadth of 

 14 inches 6 lines ; the breadth (in the same direction, transversely) of the centrum being 

 5 inches 3 lines. The vertical diameter of the middle of the articular surface of the 

 centrum is 4 inches 9 lines ; the height of the vertebra to the base of the neural spine is 

 11 inches. This spine has been worked out entire only in the above-described cervical 

 and caudal vertebras ; but there are indications justifying an estimate of its length in 

 the dorsal series, at from 6 to 8 inches. 



Thus, the dorsal vertebra, affording material for the present description, which 

 has a breadth, as above shown, of one foot two and a half inches, had a height of at 

 least one foot and a half. 



The fore-and-aft dimension of the centrum (PI. XIII, fig. 3) is 4 inches. The 

 anterior surface (ib., a), where it varies from flatness, is toward convexity, but in the 

 feeblest degree ; the posterior surface (ib., b) is very slightly, but more equably, concave. 

 The free surface of the centrum is moderately concave longitudinally ; slightly depressed 

 at /, beneath the base of the neural arch. The tissue throughout the vertebra is more 

 compact than in Cetiosaurus (Mon. cit., Tab. IX, fig. 2). 



The neurapophyses (PI. XII, fig. 1, n p) have coalesced with the centrum ; they quickly 

 narrow transversely, above their base, to a thickness of half an inch, more gradually 

 contract in fore-and-aft dimension (PI. XIII, fig. 2, % p) to two inches and a half. Over- 

 arching the neural canal (PI. XII, fig. 1, n), they meet and coalesce about one inch and nine 

 lines above the centrum, whence their compact coalesced mass rises above the crown of 

 the arch, expanding to a height of five inches (posteriorly, PI. XIII, fig. 1) before giving 

 off the neural spine (ib., % s)- 



At three inches above the base the outer surface of the neurapophysis is excavated by 

 a smooth oval cavity (ib., fig. 2, p), 1 inch 9 lines in vertical, 1 inch 6 lines in 

 transverse, diameter, and about 8 lines in depth. To this cavity was adapted the ' head 

 of the rib :' for this part there is no parapophysis, or outstanding process. Below the 

 capitular cavity the outer surface of the neurapophysis is divided from the hinder surface 

 by a low obtuse ridge or angle (ib., ib., e ) ; a broader ridge (ib., ib., a), also low 

 and obtuse, rises along the middle of the outer surface of the neurapophysis, and 

 expands to form the lower margin of the costal pit. In advance of this pit the 



