454 PROP. W. J. SOLLAS ON A NEW SPECIES OP PLESIOSATJRTJS. 



line, i. e. it is inclined forwards at an angle of 3° from the vertical ; at 

 the sixtieth (lx) vertebra (1st sacral) the spine has resumed its 

 backward inclination. 



The Bibs. 



The early dorsal ribs for about two inches from the proximal end 

 are almost straight ; they then somewhat rapidly bend into a curve, 

 which is steeper near its origin and straighter towards the end. At 

 the fifty-first vertebra the curvature of the rib has become less, in 

 the fifty-third much less ; and at the fifty-fourth the rib is straight. 

 The longest ribs are those of the forty-seventh to the fiftieth ver- 

 tebrae ; behind the fifty-second they rapidly shorten, those of the 

 fifty-sixth being only 5*4 inches, and of the fifty-ninth 2*7 inches 

 long. 



For a short distance from the head the ribs are roughened with 

 irregular longitudinal ridges, which are most marked in the anterior, 

 and absent in the last few posterior dorsal ribs. All possess simple 

 proximal ends, except the first dorsal, which gives off a short process 

 just below the head. 



Sacral Vertebrae. 



The two vertebrae regarded as sacral are the sixtieth and sixty- 

 first (lx and lxi). In them the transverse process has become very 

 short, little more than a raised facet, the surface of which, however, 

 is larger than that of the preceding transverse process of the last 

 dorsal. It obviously consists of two nearly equal parts — an upper 

 contributed by the neural arch, the articular face of which is a plane 

 surface, meeting along a horizontal line at an obtuse angle the 

 similar plane surface of the inferior moiety contributed by the cen- 

 trum. The ribs are short (1*9 inch long) and slightly expanded 

 at the distal ends. The neural spines are inclined backwards, making 

 in the sixtieth an angle of 80°, and in the sixty-first of 78°. 



Caudal Vertebrae. 



If the determination of the sacral vertebras be correct, then there 

 are five caudal vertebras, the dimensions of which are given in the 

 appended Table (page 455) of measurements for all vertebras past the 

 last cervical. The spines are broken away from them all except the 

 first, in which it is suddenly inclined backwards at a much greater 

 angle than that of the last sacral. The zygapophyses are nearly 

 vertical. 



The transverse processes are now represented merely by pits with 

 raised margins, only the upper part of which is furnished by the 

 swollen end of the neural arch. The ribs remain short ; but that of 

 the first is longer than that of the last sacral. 



