REPTILIA: VARANOSAURUS 95 



so between the fifth and sixth, the intercentral spaces are large, 

 the cartilaginous surface extending back a considerable distance 

 on the underside of the succeeding centra. Evidently there was 

 considerable mobility between the vertebrae here. 



Ribs (Plate I). — -Most of the ribs of this skeleton were found in 

 close articulation with the vertebrae, but they were so slender and 

 frail and so firmly cemented together by the matrix as they lay 

 partly folded over each other that only a few could be extricated in 

 good shape. In the figures I give illustrations of some of the best 

 of these, those found associated with the fifteenth to the eighteenth 

 presacral vertebrae. As is seen in the figures, they are very dis- 

 tinctly double-headed, the head articulating as usual in the inter- 

 central space, the tubercle to the end of the diapophysis. They 

 are very gently curved in nearly one plane, very unlike the stout 

 ribs of Casea, and they are relatively slender. Evidently, as in 

 lizards, they had a long, cartilaginous continuation. On the first 

 three or four presacrals they are little more than tubercles, gradually 

 becoming longer, and becoming free, or nearly so, on the sixth. 



Ventral ribs. — It is very evident that the whole underside of the 

 abdominal region of Varanosaurus was covered by slender and 

 numerous ventral ribs, lying close together and doubtless meeting 

 in a V-shaped angle in the median line. Only isolated patches of 

 these ribs have been recovered. In a single piece fifty millimeters 

 in length and twenty-five millimeters in width I count fourteen 

 ribs, continuous and parallel. Freed from their incrusting matrix 

 they are little more than one millimeter in diameter, and I doubt 

 not that some of them reached a length of four or five inches; the 

 longest I have observed are about three inches. 



The sacrum (Plate III; Plate IV, Fig. 8; Plate VI, Fig. 7; Plate 

 XI). — This is composed of two vertebrae, which through their mas- 

 sive ribs have a firm union with the pelvis. The spines are nearly 

 vertical, or convergent, somewhat rounded, and pointed at their 

 extremity, narrower and rather stouter than the preceding ones. 

 The zygapophyses are not very heavy; the centra are rather sharply 

 carinate below, and an intercentrum is present between the two. 

 The anterior ribs, much the larger of the two pairs, arise from the 

 anterior two-thirds of the centrum and the corresponding part of 



