OOLITIC DINOSAURS. 621 



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 77 and 78 with Plates 74 and 75 of a former 

 part of this work, 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 genns 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 Ic^uanodon (p. 508, Plates 46, 47) difi'ers 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 

 the spine of Omosaurus has been attached, in the tarsal spine of the Platypus {Ornitho- 

 rliynchm ]jaradoxus,Y\d\jQ 77, fig. 2, twice natural size). There was the same pro- 

 portion of breadth to the body of the spine ; the same sudden expansion to form the 

 base ; the same medial rising in the long axis of the base, and furrows extending 

 therefrom to the margin. But these radiating furrows are more numerous, and the spine, 

 though it is hollow as in Omosaurus, has that cavity converted by terminal apertures into 

 a canal, and this canal is traversed, as in the poison-fang of certain Ophidian Reptiles, by 

 the duct of a gland. The atfinity shown by the Monotrematous Mannnals to the Reptilia 

 in certain parts of the .skeleton is well known, and is closer in the structure of sternum, 

 coracoids, and clavicles, than in any Bird. 



