116 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



back to within a few feet of the end of the tail. Immediately in front of this 

 series of centra are broad-headed ribs with a length of 300 mm. or more, while 

 the ribs with the centra opposite the pelvis are suddenly shortened to 120 mm. 

 in length, and the rib heads are narrowed to a broad elliptical cross-section. 

 The vertebrae immediately behind the pelvis of this specimen correspond in 

 form, and particularly in form and size of the diapophyses and in their posi- 

 tion on the side of the centrum, to a point in the column not farther forward 

 than the seventy-first vertebra behind the head, or the sixth behind the pelvis, 

 of the practically continuous series of specimen 9950. (See fig. 128). 



In the vertebrae immediately behind the pelvis the width of the centra 

 transversely is somewhat less than the height, and the diapophyses are situ- 

 ated about one-third of the distance up the sides of the centra. The height 

 of the neural arches is less than that of the centra, and the thin, broad spines 

 are bent backward. 



In passing backward through the caudal region from the pelvis to the thir- 

 tieth vertebra back of the femur, as here situated, the centra decrease very 

 little in height but become much narrower transversely, and in the region of 

 the thirtieth vertebra become relatively short inf eriorly ; the diapophyses rise 

 to the middle of the centra, become reduced to small round knobs and disap- 

 pear; the neural spines become shorter, are slightly wider distally, and begin 

 to stand erect. The change from the recurved to erect position of the arches 

 takes place at the thirtieth vertebra. The upper arch of the twenty-eighth 

 vertebra turns backward as do those of all anterior to it, on the thirtieth the 

 arch is erect and on the thirty-first it bends forward. Behind this point to the 

 fifty-third vertebra the short upper arches all turn forward. The arches of 

 the fifty-third and fifty-fourth, the last ones present in this specimen, are erect 

 but not curved forward. In the region immediately behind the point where 

 the upper arches begin to turn forward, the centra are slightly wedge-shaped, 

 being shorter anteroposteriorly at the lower side. Though the diapophyses of 

 the thirtieth vertebra are rather prominent no lateral apophyses are present 

 behind this point. A short distance back of the bend the middle of the lateral 

 face of each centrum bears two parallel anteroposterior ridges about twenty 

 millimeters apart and separated by a shallow depression. 



The changes in form of the caudal vertebrae which have been mentioned 

 seem, as far as can be judged, to be connected with fairly definite changes in 

 the curvature of the caudal region as shown in this specimen. As the series 

 of vertebrae lies in the matrix the tail is bent slightly upward as far back as 

 the thirtieth vertebra but from that point backward it is curved downward. 

 At the point where the downward curvature begins the upper arches suddenly 

 stand erect and then turn sharply forward, the diapophyses disappear, and the 

 anteroposterior diameter of the inferior side of the centra becomes relatively 



