60 PROF. H. G. SEELEY ON" A NEW 



Cambridge bones. The length of the centrum is the same, and its 

 wedge-like character identical. The surface behind the transverse 

 processes, which is not clearly seen in the Cambridge bones, is found 

 to form a wedge with lateral excavations, which extend forward 

 under the posterior expansions of the transverse processes. 



In several vertebrae there are slight pits at the base of the anterior 

 margin of the neural spine, and well above the large deep depres- 

 sion bordered by the zygapophysial facets, beween which the sharp 

 anterior margin of the neural spine is prolonged. The notch be- 

 tween the zygapophyses only extends for their anterior third. 



A few vertebrae have the neural spine preserved, but it is not 

 perfect. In one (fig. 2) it is 16 1 centim. high, 9 centim. wide at the 

 base ; it contracts a little in the middle, chiefly by concavity of the 

 posterior border, widening a little above, so as to make both margins 

 concave. 



All the British-Museum specimens show the facet for the head of 

 the rib, though it varies much in character. At first it is small 

 (&, fig. 2, p. 58) vertical, and low in position. Gradually ascending, 

 it widens and becomes more circular. And when the transverse 

 processes become horizontal, the superior and anterior margins be- 

 come greatly elevated. In the hinder part of the series the facet 

 becomes small and transversely oval. 



I have seen neither cervical nor caudal vertebrae which present 

 this tj r pe. The Cambridge specimens were obtained by Mr. Keeping 

 in 1866, and brought to the Museum with the coracoid lately 

 described ; but he has no recollection of their having been asso- 

 ciated with that bone. But in view of the likelihood of these ver- 

 tebrae pertaining to the " Iguanodon Seelyi" I have refrained for 

 the present from giving a specific name to the specimens. 



The characters on which I establish the genus Sphenospondylus 

 for these remains are the laterally compressed form of the base of the 

 dorsal centrum, the depressed form and character of the neural arch, 

 the upward inclination of the transverse processes, and the condition 

 of the facet for the head of the rib in rising so as to be placed be- 

 tween the transverse process and the anterior zygapophysis. These 

 characters clearly differentiate it from Iguanodon, which is the only 

 genus with which it can be compared, supposing that we take 

 Iguanodon Mantelli as the type (figs. 4 & 5). But the genus has 

 since been enlarged to include such types as Iguanodon Prestwichi 

 and /. Seelyi, both of which differ from the type in well-marked and 

 varied characters. What the significance of those differences is 

 may, I fancy, be determined by comparing together existing genera 

 of animals, and noticing the nature of the characters by which they 

 differ. Judged in this way, I think it possible that both these 

 species might be referred to new genera ; and from such a point of 

 view I conceive of these vertebrae as indicating a new genus. But 

 if we take the older conception of a genus, which is anatomical and 

 not zoological, and more a matter of palaeontological convenience 

 than a step in evolutionary history, we may rank all these forms 

 under the one name Iguanodon. It is a matter on which there is 



