20 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 77 



Chevron. — The first chevron is carried on the fourth caudal as 

 in Dyoplosaurus and all are coosified with the vertebral centra. 

 The anterior chevrons are intervertebral but posteriorly articulate 

 entirely with their respective vertebrae. These bones of the anterior 

 half of the tail have the proximal articular ends bridged across with 

 bone but more posteriorly these ends are distinct. The anterior 

 chevrons are long and bladelike with slightly expanded ends, but 

 as the shaft shortens posteriorly their distal ends become corre- 

 spondingly enlarged as shown in Figure 13. 



The haemal canal is large anteriorly but becomes very small in 

 the posterior part of the series. 



Ribs. — There are parts of no less than 28 ribs present, half of 

 which are complete. These pertain to both right and left sides 



^ representing all sections of the body. 



The outstanding features of the ribs 

 are their general massiveness and 

 wide spread. The thoracic ribs, 

 when articulated, rise as high as the 

 top of the spines, thus forming an 

 exceedingly broad back and great 

 girth. 



Of the above-mentioned ribs six 

 are regarded as cervical, the first 

 pair being firmly coossified with the 

 coalesced atlas and axis, as shown in 

 Figure 6. They are single headed, 

 with widely expanded ends which 

 not only articulate with the centrum 

 of the atlas but are in contact with 

 the anterior end of the axis as well. The shaft is stout, sub-ovate 

 in cross-section, with a bluntly pointed distal extremity. The rib of 

 the right side is 130 millimeters long. 



The cervical rib illustrated in Figure 14 is tentatively identified 

 as the second of the left side. It was found widely separated from 

 the axis, but the spread of the tubercular and capitular processes 

 is in agreement with the dia- and parapophysial facets on the axis. 

 Its slightly increased length over the first cervical rib corroborates 

 this assignment. On the other hand, when compared with the second 

 cervical rib of Panoplosaurus mirus as described by Sternberg,^^ 

 such differences are found, especially in the proximal end, as to raise 

 a question as to its really being the second of the series. This rib has 

 a greatest length over all of 143 millimeters. The tubercular and 

 capitular processes are of about equal length, the former as usual 



Figure 14. — Second? left cervical 



KIB OF PALAEOSCINCUS RUGOSIDENS. 



Type. No. 11868. U.S.N. M. A, Lat- 

 eral VIEW ; B, ventral view. Both 



FIGURES one-third NATURAL SIZE 



'Trans. Roy. Soc. Canada, vol. 15, 1921, pi. 1, figs. 3. 



