ART. 16 FOSSIL REPTILES FEOM MONTANA GILMOEB 1 1 



and can be identified as P, costatus. None of these, however, shows 

 sculpturing of the crown surface. From this brief review it is 

 quite apparent that the teeth are near enough alike to indicate con- 

 generic relationships, but are sufficiently unlike, in the light of our 

 present knowledge, to show them to pertain to distinct species. 



Three other species of this genus have been proposed at various 

 times, Palaeoscincus asyer Lambe,® P. lotus Marsh," and P. tnagoder 

 Hennig.^^ The last is said by Hay ^^ to be a nomen nudum and may, 

 therefore, be dismissed from further consideration. The type of 

 P. latus^ from the Lance formation, is a stegosauroid style of tooth 

 that can at once be distinguished from the teeth of P. rugosidens 

 by its low crown and the regularity of its denticles. (See pi. 4, fig. 

 4. ) P. as'per may likewise be distinguished by the more numerous 

 denticles, sides of crown more conspicuously ridged, and a double 

 row of denticles at one end of the cutting edge. (See pi. 4, fig. 2.) 



Atlas and axis. — The atlas and axis are fused together by their 

 centra, nueral arches, and spines, a condition previouslj^^ observed by 

 Sternberg ^^ in Panoplosaurus mirus. The English Scelidosaurus ^* 

 likewise has a fusion of the atlas and axis. In Stegosaurus these 

 bones remain distinct. 



The cup on the anterior extremity of the atlas for the reception 

 of the occipital condyle is deep and subcircular in shape. It has a 

 depth of 31 millimeters and a greatest estimated transverse diameter 

 of 57 millimeters. The atlas is long, broad, relatively low and with- 

 out ventral keel. It bears strong, coosified, single-headed cervical 

 ribs that project downward and strongly backward, as shown in 

 Figure 6A. It is estimated that the atlas centrum had a length of 

 about 88 millimeters. 



The pedicals of the neuropophyses set well back from the anterior 

 margin of the centrum. (See fig. 6A.) On the posterior borders they 

 develop a thin process that extends upward, backward, and inward. 

 These converge and unite medially with the neural spine of the axis 

 arching over the anterior border of the neural canal, as well as the 

 vertebral arterial canals. Above and posterior to the vertebral 

 arterial canal, these processes are completely fused with the axis, 

 leaving hardly a trace of the anterior zygapophyses of the axis or 

 the posterior zygapophyses of the atlas. A broad anterior process 

 of the neurapophyses extends inward above the neural canal but does 



»Lambe, L. M., Geol. Surv. Canada, Cont. Can. Pal., vol. 3, pt. 2, 1902, p. 54, pi. 17, 

 fig. 5. 



" Marsh, O. C, Amer. Jour. Sci., ser. 3, vol. 44, 1892, p. 173, pi. 8, flg. 3. 



11 Honnig, Edwin, Naturw. Wochenschr., new ser., vol. 18, no. 51, 1919, p. 771. 



"Hay, O. P., Second Bibliography of the Fossil Vertebrata of North America, vol. 2, 

 1919, p. 237. 



13 Trans. Roy. Soc. Canada, vol. 15, 1921, pp. 93, 94, pi. 1, flg. 1. 



" A monograph of the Fossil Keptilia of the Liassic formation, pt. 2, Paleontographical 

 Soc, 1863. 



