176 BRITISH FOSSIL REPTILES. 



from the bottom of this pit rises the thick and strong posterior ridge of the 

 neural spine. 



Measured from the origin of this ridge, the spine rises to a height of one foot ; 

 the breadth of the spine at its mid-height is three and a half inches ; but it expands 

 as it rises to twice that breadth ; and both the sides and summit of this expanded 

 part have suffered loss. 



The least injured part of this extraordinarily complex bone is the right side : 

 but sufficient remains of the left side to indicate corresponding ridges, plates, 

 cavities and other sculpturings of the osseous substance, the characters of which I 

 have here attempted to describe. 



I may remark that the Saurian vertebrae hitherto discovered, which have the 

 convex and concave terminal surfaces of the centrum on opposite sides to those 

 which they hold in modern Crocodilia, and which have suggested to V, Meyer the 

 term 8treptospo?idylus ; also differ from the true Crocodilia by a complexity and 

 development of the neural arch, which indicates their position to be among 

 Binosauria, 



SUPPLEMENT TO CHAPTER ll.—IcUhyopterTjgia. 



Ichthyosaurus fortimanus, Owen. 



In the pectoral paddle of Ichthyosaurus latimamis {ante p. 83, PI. XXIX, fig. 1), 

 of which the vertebral characters are described and figured (ib., figs. 2 and 7), five 

 digital series are recognisable by their angular characters, besides the radial and 

 ulnar marginal smaller rounded series. In IchthyosaicrusfoHimanus,-wiih a paddle 

 of equal breadth in proportion to the length, there are four digital series according 

 to the relative size and angularity of the phalanges ; and, if a fifth series should 

 answer to the fifth (ulnar) digit of Ich. latima,nus, its phalanges are reduced to the 

 smaller size and rounded shape of a marginal series ; but as they are bordered by 

 a true marginal series of still smaller rounded ossicles, such reduction of the 

 representative fifth or ulnar digit adds a second specific distinction to the pectoral 

 paddle of Ich. fortimanus ; the relative breadth of the fin being mainly duo to the 

 larger relative size, especially breadth, of the phalanges of the 1 — 4 digits. 



Ichthyosaurus longimanus, Owen. 



In the same Plate is represented a well-preserved pectoral fin, as remarkable 

 for its relative length as those of the two above-named species are for breadth ; 

 yet the five normal digits and the marginal supplementary series enter into its 

 formation. The phalanges here are notable for their great number in each digit, 



