442 Prof. 11. G. Seeley on the hiterhchlng 



Society's Monograph, 1881, pi. xxi. In 1891 Dr. Eberliard 

 Fraas figured two prezygapophyses in liis memoir on Lias 

 Ichthyosaurs (pi. iii. fig. 6). 



In 1869 ('Index to Aves, Ornithosauria, and Heplilia/ 

 p. Ill), in describing Ichthyosaurus megalodeirus from the 

 Oxford Clay, I found the neural arches preserved in the sixth 

 and seventh cervicals, and displaced laterally, so as to show the 

 lateral zygapophyses, which are " long and oblique, looking 

 upward and inward^'; but I am unable to affirm that this 

 characteristic prevailed in all the twenty-six cervical vertebrae, 

 though the unusual length of the neck, permitting lateral 

 movement, makes such a condition probable. 



Examination of the skeletons from the Lias has shown that 

 the antero-posterior articular union between adjacent neural 

 arches is made by a single flat median facet, vertically ovate, 

 inclined at an angle of 45° in the dorsal and caudal regions. 

 The facet varies a little in proportion of length to width. 

 It is always immediately above the neural canal. In some 

 anterior examples the facet is indented by tiie neural canal 

 beneath it, so that it acquires a horseshoe type of form. In 

 such specimens the neural spine is short and depressed and 

 the neural arch is small. Professor Eb. Fraas, in tab. v. 

 fig. 11 ' Ichthyosauria,' 1891, represents a single vertically 

 ovate facet with an appearance of vertical division, in the 

 neural arch of an Ichthyosaur. 



In January 1889 Mr. A. N. Leeds, F.G.S., obtained and 

 submitted to me the first known British example of an 

 isolated neural arch from the Oxford Clay of Fletton, which 

 since then has been referred to in my lectures as Ophthalmo- 

 saurus iceni'cus (figs. 1 & 2). 



The specimen measures 4^ inches from the neuro-central 

 suture to summit of the neural spine. The neurapophyses 

 are compressed from side to side, half an inch wide in front, 

 where the neural interspace between them is eight-tenths of 

 an inch wide. The processes are more compressed from side 

 to side posteriorly. The neuro-central sutural border is convex 

 from front to back (fig. 1). In axial aspect the processes 

 converge upward to arch over the neural canal, which appears 

 to have been triangular and rather higher than wide (tig. 2). 

 In lateral aspect the processes are concave on both the front 

 and back borders, to define the interspaces for the escape of 

 the intervertebral nerves (fig. 1). 



Above the neural canal is the single facet by which the 



