REPTILIA: CASEA 121 



transversely concave on the upper surface, and has a conical 

 cavity on the posterior side, which in life was in apposition with the 

 concavity of the axis, and was for the notochord, which, however, 

 did not extend through the bone. Very evidently the intercentra 

 of both the atlas and the axis were relatively large bones. 



Ribs (Plate XVII). — The ribs of Casea are remarkable for their 

 size and length. They were found in all three specimens in posi- 

 tion as far forward as the sixth or the seventh ; the more anterior 

 ones were not recovered and have necessarily been restored in the 

 mounted specimen, and I suspect that they were somewhat 

 longer on these anterior vertebrae than they have been restored. 

 The first four presacral vertebrae have the ribs firmly co-ossified 

 with the arch and centrum, leaving a small foramen between head 

 and tubercle. The ribs of the fifth presacral were less firmly 

 united and in the two specimens examined had dropped away, 

 though their union is seen to be a sutural one. The ribs of the 

 first presacral are rather slender and are directed a little forward 

 and upward, their extremities being higher than their capitula. 

 The next three pairs increase rapidly in length; they are directed 

 outward, a little forward, and then curve downward strongly at 

 their extremities. Like all the preceding ribs preserved they are 

 remarkably thick and stout. The longest ribs of the series occur 

 at the middle of the presacral series. They are, as preserved, for 

 the most part quite regularly curved, nearly cylindrical, very 

 stout, tapering a little distally. The tubercular part is not sharply 

 indicated as it lies against the end of the diapophysis, nor is there 

 a distinct facet on any of the centra for the union of the capitulum, 

 which must have been quite in the intercentral space, a little 

 below the middle of the centrum, leaving a very considerable 

 foramen in the articulated condition. The distal end is truncate, 

 indicating a cartilaginous cohtinuation, but this continuation was 

 probably very short, since the ribs in articulation for the most 

 part curve inward at the lower end and may be compared with 

 the shorter ribs and costal ribs of the lizards combined. Evidently 

 the underside of the body between the ribs was quite flat, other- 

 wise the belly would have been strongly protuberant below the 

 level of the pelvis and pectoral girdle. There is not the slightest 



