﻿96 



FOSSIL REPTTLIA OF THE 



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 XXIII, 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, 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 XXIV, 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 6 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 

 preserved portions of each spine, and were probably continued to, or near to, the pointed 

 end. An additional advantage as a lethal or piercing weapon must have been derived 

 from this two-edged structure. 



In the right spine (fig. 1) the length preserved is 14 inches; in the left spine 

 (fig. 3) the length preserved is 10 inches. Each spine may be estimated to have been 

 upwards of 20 inches in length when entire. 



The transverse section taken from the broken end of the left spine (fig. 4) gives 4 inches 

 and 3^ inches in the two diameters : the broken end of the better preserved spine gives 3 

 inches and 2f inches in the two diameters ; the spine approaches to a circular section as 

 it nears the pointed end. The texture of the outer inch is a compact bone susceptible 

 of a high polish ; it becomes finely cancellous within a few lines of the central cavity, the 

 section of which at the part cut, viz. 8| inches from the base of the spine, gives 1 inch 

 6 lines, and 1 inch 3 lines, in the long and short diameters. 



The close correspondence of the present fossil in general form, in basal modifications 

 for attachment, and in texture, with the spine, probably left carpal, of Omosaurus armatus, 

 will be obvious on comparison of Plates XXIII and XXIV with Plates XXI and XXII 

 of the former part of this Monograph, treating of that species ; and such correspondence 

 may be deemed to support the provisional reference of the carpal (?) spines from the 

 Kimmeridge Clay of Wootton Bassett to the same genus as that from the Kimmeridge 

 Clay of Swindon ; they manifestly indicate a distinct species on the above hypothesis of 

 their nature. 



The osseous core of the carpal spine in Iguanodon (' Wealden Reptilia,' Sup., No. 4, 

 Pal. vol. for the year 1871, issued in 1872, Plate II, fig. 2) differs chiefly in its relative 

 shortness or speedier diminution from the base to the apex. 



After a comparison of these fossils with all the examples of carpal and tarsal spines in 

 existing vertebrates, I found the nearest resemblance to the basal expansion, by which 



