620 BRITISH FOSSIL REPTILES. 



Qenus — Omosaurus. 



[Continued.) 



Species — Omosaurus hasti(jer, Owen. (' Dinosauria,' Plates 77 and 78.) 



If the gi'ouncls assigned in a former part of this worlv (p. 577) for the probable 

 homology of the unsymmetrical spine figured in Plates 74 and 75, which spine was 

 found with the bones of the fore-limb of Omosaurus armatus, should be deemed to 

 warrant such conclusion, a similar one may be provisionally accepted as applicable to 

 the pair of spines of similar size and character discovered in the same division of the 

 Kimmeridge Clay, in the Great Western Railway Cutting at Wootton Bassett, Wiltshire, 

 briefly referred to at p. 577. 



Many large Saurian fossils were collected from the sections of Kimmeridge Clay at 

 that time exposed ; but none have reached me save the subjects of the present Mono- 

 graph, which were there obtained by William Cunniugton, Esq., F.G.S., and have passed 

 with the rest of his collection into the possession of the British Museum. The apical 

 portion of each spine has been broken away, but the degree of decrease from the base 

 affords satisfactory grounds for the restoration given in Plate 78, the ratio of decrease 

 being less in the present species than in the almost perfect spine of Omosaurus armatus 

 (Plate 74). 



The base of the spine (Plate 78, h) expands from the body, «, more suddenly and in a 

 greater degree in Omosaurus hastiger. It is suboval in form and, as in Omos. armatus, 

 its plane is oblique to the axis of the spine. The long diameter of the base is 9 inches, 

 the short diameter is 7 inches. 



The articular surface is divided into two unequal facets by a low ridge of the base 

 (Plate 77, fig. 1, r, r) parallel with the long diameter of the base; each facet is feebly 

 convex lengthwise, less feebly concave transversely. The surface for attachment is 

 roughened by low short ridges diverging from the long ridge, r, and is irregularly pierced 

 by vascular canals ; the borders are thick and irregularly notched. 



The body of the spine is continued more directly from one end (Plate 78, figs. 1, 

 2, 3) of the oval base, a, fig. 2, sloping and expanding more gradually to the opposite 

 end of the base, b, fig. 2. 



The body of the spine is a full oval in transverse section (ib., fig. 4), pointed at each 

 end, where the two opposite edges, d, e, are cut. The anterior edge (fig. 1, d), begins 

 about G inches beyond the anterior produced part of the base; the posterior edge 

 (fig. 3, e) begins about 2 inches from that end of the base. Both edges extend along the 

 presei'ved portions of each spine, and were probably continued to, or near to, the pointed 



