AKT. 16 



FOSSIL REPTILES PROM MONTANA GILMORE 



19 



Whether these combined outer ends gave support to the ilium can- 

 not be determined from this specimen. The wedge shape of the an- 

 terior centra, especially the third (fig. 12A), indicates a rapidly 

 dropping tail, a feature also found in the Jurassic Stegosaurus. 



In all of the anterior caudals the arch is massive and the short 

 spines are heavy, angularly rounded in cross-section with expanded 

 extremities. In the mid-caudal region, however, the spines are flat- 

 tened with slight trans- ^ 

 verse dilation of their 

 upper ends (fig. 13.) All 

 of the spines on the ante- 

 rior two-thirds of the tail 

 strongly overhang the 

 centra. In the smallest 

 vertebra present the spine 

 no longer stands upright 

 but persists as a low, 

 rounded ridge without 

 lateral expansion, termi- 

 nating posteriorly in a 

 bluntly rounded point 

 projecting directly back- 

 ward beyond the posterior 

 zygapophyses which are 

 fast becoming sessile. 



No indication of a 

 " tail-club " was found 

 and but two vertebrae 

 from the anterior half of the tail showed indication of ankylosis. 

 These have their centra fully coossified, a condition, as indicated by 

 the deformed nature of the bones, brought about by an injury. 



Figure 13. — Median caudal vertebra of Palaeoscin- 

 CUS RUGOSIDENS. TYPE. No. 11868, U.S.N.M. A, 

 Lateral view ; B, Anterior view ; Ch., Chevron. 

 Both figures about one-third natural size 



Measurements of caudal vertebrae 



No. of vertebra in series 



1 



2 



3 



5(?) 



7(?) 



8(?) 



9(?) 



11(?) or 12(?) 



14(?) 



15(?) 



(?) 



Greatest 



length of 



centra 



Mm. 



67 

 52 

 49 

 44 

 57 

 58 

 44 

 56 

 52 

 56 

 66 



Greatest 



width of 



centra 



(post, end) 



Mm. 

 107 

 107 

 103 

 100 



85 

 88 

 85 

 86 

 81 

 66 



Greatest 

 width of 

 transverse 

 processes 



Mm. 

 404 

 367 

 310 

 216 

 194 

 183 



90 



Greatest 

 height 

 over all 



Mm. 

 211 

 208 

 200 

 190 



172 



107 



135 



87 



Remarks 



Coossified. 

 Centrum only. 



