208 Systematic Paleontology 



This tooth resembles somewhat that of Palceoscincus costahis Leidy/ 

 from the Judith Eiver beds, though the type of Palceoscincus is slightly 

 smaller than that of the present species. The swelling shoulder in 

 Priconodon is more prominent and rounded than in Palceoscincus, and 

 in the latter the cusps are much sharper and more prominent, though 

 less numerous on one edge of the crown. The median ridge of Pricono- 

 don is also lacking. 



The tooth of Priconodon resembles those of Diracodon and Stegosaurus 

 in the rounded shoulder, but has the blade of the crown more sharply 

 compressed and is very much larger. The dimensions of the former are : 

 Diracodon, 5mm. wide; Stegosaurus, 5.5 mm. (measured from the fig- 

 ure). A specimen, ISTo. 2606, from the collection of Goucher College, 

 Baltimore, is a relatively immense tooth, though badly worn through 

 use and subsequently, so that except for the general shape, the distinctive 

 characters are not clearly discernible. Its dimensions are as follows : 



Width 15.7 mm. 



Height of crown 14.6 mm. 



Thickness of crown 9.3 mm. 



The two last measurements have become less through abrasion. This 

 tooth represents a much larger animal, for an individual has teeth of 

 approximately the same size throughout, if one may judge from the jaws 

 of Diracodon and Stegosaurus. There are, however, in the collection of 

 Goucher College, Baltimore, specimens intermediate in size, and all so 

 worn as to show no clearly defined specific characters which would serve 

 to separate theni from the type. These specimens, five in number, are 

 all from the blue charcoal clay of Coffin's Old Engine Bank, Swamp 

 Poodle, near Muirkirk, Maryland. The locality of the type is also the 

 Swamp Poodle, but the precise locality and level are not given. 



From the Arundel blue charcoal clay of Contee, Maryland, comes 

 specimen No. 3101, of the Goucher College collection, the centrum of a 

 dorsal vertebra (pi. xx, fig. 6), unlike anything else in the entire mass of 

 Arundel material. It represents a young animal, since the neural arch 

 had not yet coossified with the centrum. The centrum is opisthoccelous, 

 the anterior articular face being plane; the posterior a moderately deep 



^ Trans. Amer. Phil. Soc, vol. xi, 1860, pp. 146-7, pi. ix, figs. 49-52. 



