H. GOVIER SEELEY ON MACKUROSAURUS SEMNUS. 441 



to remain there, I do not see my way to placing it in any one 

 of the subdivisions of that group. 



The vertebrae are in different states'of mineralization — some show- 

 ing no indications of phosphatic infiltration, while in others this 

 process has gone on to a considerable extent. 



The preservation of the specimens is occasionally such that I can- 

 not feel certain that all are arranged in exactly their true order of 

 succession. The first vertebra preserved is an early caudal much 

 decomposed on one side, and considerably abraded, with only the 

 base of the neural arch preserved, and an indication of the antero- 

 posterior extent of the fractured transverse process. Its imperfect 

 preservation is due to the fact that the bone is open and cellular, 

 and but slightly mineralized with phosphate of lime. 



The articular surface of the centrum is deeply cupped anteriorly, 

 and is more expanded in front than behind, where it forms a large 

 hemispherical ball. The sides of the centrum are compressed, and 

 converge towards the ventral surface, where they form a median 

 rounded ridge. The length of the centrum is 8 inches, and of this 

 the unarticular side of the centrum measures 5J inches ; the depth 

 from the neural canal to the base of the hinder part of the centrum, 

 as preserved, is fully 5J inches, and in front was probably more. 

 The side is smooth, with some longitudinal vascular impressions, 

 gently concave from front to back. The basal keel is well rounded 

 from side to side, and gently concave from front to back. 



The transverse process appears to have been 3| inches in antero- 

 posterior extent at its base, where fractured. It was strong. 



The neural canal was smooth and narrow. 



What are probably pedicles for the neural arch extend to the 

 anterior border of the cup. This process on the right side is com- 

 pressed, less than half an inch thick, with an antero-posterior ex- 

 tent of 2 J inches. 



The worn fragment of the next vertebra is 7J inches long. On 

 the third the transverse processes have disappeared. The anterior 

 cup of this vertebra, as preserved, is 5| inches wide ; and the cen- 

 trum does not exceed that length ; but the ball and the margin of 

 the cup are both broken. The neural canal is more than an inch 

 wide. On each side of it the centrum gives off strong compressed 

 pedicles 2 inches in antero-posterior length, half an inch thick, 

 inclined a little towards each other, and approaching to within half 

 an inch of the anterior border, as preserved. These pedicles are not 

 mueh more than half an inch high, and were probably separated 

 from the neural arch by a horizontal suture. 



The centrums now become rapidly smaller in diameter and flat- 

 tened on the visceral surface. The articular cup remains as deeply 

 marked ; but the ball appears to have a depressed, flattened margin 

 an inch wide around the elevated central boss, as in existing croco- 

 diles. That numbered 8 is 6^ inches long and has the cup 4 J inches 

 deep. No. 11 is 5^ inches long, has the cup much less deep, but the 

 ball is not at all preserved. The centrum has now acquired a dice- 

 box form. No. 12 is as long, but the centrum is smaller, the cup 



