PELVIC AECII OF ICHTHYORNIS. 163 



They correspond with only three such processes in the type of Ichthy- 

 ornis. Behind these processes, the central portion of the sacrum is 

 thickened below, and sends off a strong transverse process on each side, 

 nearly at right angles with its axis. Behind this, are three pairs' of trans- 

 verse processes directed well backward. The second of these is preserved 

 in the specimen, and formed a strong process for attachment with the 

 ilium. The last pah- of processes were short, and the independence of the 

 vertebral centrum to which they were attached is indicated by a tuber- 

 cular thickening at the point where the last sacral centrum has coalesced 

 with the preceding. The posterior articular face of the last centrum is 

 somewhat concave, and is nearly semi-oval in outline, being strongly 

 flattened above for the neural canal. 



Measurements of Sacrum. {Ichthyornis dispar, No. 1450.) 



Length of sacrum, 26.2 mm 



Vertical diameter of anterior end of first centrum, 3.0 



Transverse diameter of anterior end of first centrum, 3.2 



Least transverse diameter of centra, 1.2 



Vertical diameter of posterior end of last centrum, 1.2 



Transverse diameter of posterior end of last centrum, 2.0 



Greatest transverse diameter of sacrum, 10.5 



Measurements of Sacrum. (Apatornis celer, No. 1451.) 



Length of portion preserved, 27.5 mm 



Transverse diameter of last centrum at articulation, 2.5 



Vertical diameter of last centrum at articulation, 1.8 



Vertical diameter of sacrum, near proximal end, 1.0 



The Pelvic Bones. (Plate XXXII.) 



The pelvic bones in Ichthyornis (Plate XXXII, figures 2 and 3) are 

 strongly coossified with each other. The ilium is obtusely rounded in 

 front, and its antero-superior border is separated a short distance from its 

 fellow. The pre-acetabular part of the ilium is concave externally, and 

 considerably longer than the posterior portion. The ischium is expanded 

 medially, and extends further back than the ilium. It is not united with 

 the ilium posteriorly, thus agreeing with the corresponding part in Hesper- 

 ornis. The pubis has no distinct anterior process, but the post-pubic 

 element is elongated, and its distal portion free. 



