ART. 16 FOSSIL KEPTILES FROM MONTAN^A GILMORE 23 



ribs as representing the processus uncinatus, but I believe he was mis- 

 taken in this. A more logical explanation, it seems to me, is the one 

 given by Brown that this enlarged area on the anterior ribs may have 

 served for attachment of the heavy shoulder muscles in Ankylosaurus. 



Posteriorly the ribs become progressively more slender with pointed 

 distal extremities. There is evidence that at least three of the pos- 

 terior dorsals had the ribs fully coossified with the neural arch as 

 shown in Figure 11. So complete is this coalescence that the line of 

 demarcation between the two bones can scarcely be detected. These 

 most posterior ribs are exceptionally wide and thin below the T-shaped 

 section of their upper portion. 



In addition to the above-described ribs there are three single- 

 headed ribs of the type of the one illustrated in Figure 15D. They 

 have a roughened rugose articular proximal end slightly bowed from 

 end to end, shaft of moderate width, tapering to a pointed end. I 

 am unable to determine their proper position in the skeleton. That 

 they do not pertain to the sacro-dorsals seems to be indicated by the 

 flat, wide ends found attached to the blade of the ilium (fig. 3, 

 pi. 7) , whereas these have narrow pointed ends. The most perfect one 

 of the three which lacks the extreme distal end measures 350 milli- 

 meters in length. 



Ilium. — The preacetabular portion of the right ilium and a few 

 scattered, much-worn fragments are all that was preserved of the 

 ilia. This anterior blade is platelike, thickened, nearly straight 

 on the inner border, gradually thinning toward the anterior and 

 outer margins, the latter presenting a sharp edge. The anterior 

 end is obtusely pointed, its most anterior projection being well 

 toward the inner side of the bone; externally the border rounds off 

 toward the laternal margin as shown in Plate 7, Figure 3. The 

 upper surface of this portion is smooth, slightly convex from side 

 to side; the under surface is concave both transversely and antero- 

 posteriorly. 



There is no indication of dermal plates having been united to the 

 superior surfaces of the ilium as in Stegopelta^ although on the outer 

 half of the mid part of this section of the ilium there are shallow 

 transverse grooves, probably for blood vessels suggesting a cutaneous 

 investment that was closely applied to this surface of the ilium. 

 Lull ^° has noted a similar condition on the ilia of Nodosaurus. 



On the ventral side the distal ends of three posterior ribs remain 

 securely coalesced with this surface of the ilium as shown in Plate 

 7, Figure 3. The end of the anterior rib projects slightly beyond 

 the margin of the ilium, the remaining two terminating an inch or 

 more inside its border. 



=0 Lull R. S., Amer. Journ. Sci., vol. 1, 1921, p. 105. 



