448 PROP. W. J. SOLLAS ON A NEW SPECIES OT PLESIOSA.TJRTT8 



prolongation extends with a downward direction as far back as the 

 posterior edge of the centrum to which it belongs. 



Near the articular ends the centrum is roughened by a few small 

 irregularly scattered tubercles, which become larger and more nume- 

 rous in succeeding vertebra? down to the twenty-fifth. The neural 

 spine has been broken away • so that the total height of the ver- 

 tebra cannot be determined. The line between the zygapophyses is 

 1*9 inch from the base, and 0*9 inch from the neuro-central suture. 



vii. The seventh vertebra has a total height of 2-95 inches ; the 

 centrum is 1*375 inch long and 1-5 high. The well-marked neuro- 

 central suture is 1*1 inch from the base. The tubercles near the 

 articular ends have become larger and more numerous. The rib is 

 distinctly hatchet-shaped, and consists of a blade-like upper part and 

 a lower handle-like horizontal process ; a deep incision separates the 

 handle from the blade in front, and the front end of the handle does 

 not reach the anterior edge of the centrum by about an inch. The 

 posterior margin of the blade slopes gradually down, and curves 

 gradually into the handle, the posterior prolongation of which ex- 

 tends a short distance beyond the posterior edge of the centrum, 

 from which the rib proceeds. 



The anterior zygapophysis is, as in the other anterior cervical 

 vertebrae, turned inwards and upwards ; below the line of the zyga- 

 pophyses the neural arch is ridged in a direction crossing obliquely 

 from the anterior edge of the anterior zygapophysial facet down- 

 wards to the posterior edge of the neuro-central suture, the ridges 

 being most marked near their origin and termination. The distance 

 from the anterior to the posterior zygapophysis is 2*3 inches. Prom 

 the line of the zygapophyses to the base of the centrum is 2*0 inches, 

 to the top of the spine 1*35 inch. 



The neural spine has somewhat the outline of a Phrygian cap seen 

 in profile ; it has a gentle convex slope backwards in front, and a 

 short sigmoid curve behind ; it rises from the middle of the length 

 of its centrum, and hangs over the anterior quarter of the centrum 

 next behind. It is smooth below, but roughened towards the distal 

 end. 



The vertebrae increase in size and change in the relative size of 

 their parts as they pass backwards : down to the fifteenth (xv), pro- 

 bably to the twenty-second (xxn), the articular face of the centrum 

 is an ellipse, with the major axis vertical (d.v.) ; at the twenty-third 

 (xxiii) the diameters are about equal, and continue so to about the 

 twenty-fifth (xxv), beyond which the horizontal diameter (1.1.) be- 

 comes the larger, and continues to increase over the vertical down 

 to and beyond the end of the cervical series. The neuro-central 

 suture becomes more sharply inflected in the middle, so that in the 

 fifteenth (xv) the middle curve of the tricurvate line becomes trans- 

 formed into a right angle. The zygapophysial facets acquire by 

 degrees an entirely horizontal position ; they seem to have done so 

 in the fifteenth vertebra. 



The neural spines increase more rapidly in size than the centra, 

 and considerably change their form ; at the eighteenth (xvm) the 



