448 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



provisionally to a single species under the name of Agathaumas milo^ 

 but are here described under Madrosaurus occidentalis. The remaining 

 specimens fall into two series. In the one, the bones are occupied by a 

 heavy mineral and the surfaces covered by a white layer, which is marked 

 by irregular ridges, as though produced by deposit along the lines of 

 small adherent foreign bodies. In the other set, the bones are lighter, 

 more spongy, and not covered with the white layer ; some of them are 

 stained by the sesquioxide of iron. Both present vertebras and limb- 

 bones, which are related appropriately as to size and structure 5 that is, 

 the larger limb-bones have the same mineral character as the larger ver- 

 tebrae, and the smaller as the smaller. These limb-bones represent cor- 

 responding parts in the two, and, differing widely, confirm the belief in 

 the existence of two species indicated by the different types of vertebrae. 

 In these fossils, then, I see evidence for the existence of two species of 

 two genera, which I name, the larger Polyonax mortuarius, the smaller 

 Cionodon arctatus. Both genera present a solid cancellous filling of 

 femora, tibise, and other long bones, and hence differ from such genera 

 as Hadrosaurus, Hypsibema, Lcdaps, and others. Cionodon differs in 

 dentition from all Dinosauria where that part of the structure is known, 

 but it remains to compare Polyonax with Troodon and Palmoscincus of 

 Leidy, which are known from the teeth only, while no portions of denti- 

 tion are preserved with the specimens at my disposal. 



Char. gen. — Established primarily on a portion of the right maxil- 

 lary bone, with numerous teeth in place. The posterior portion exhibits 

 a suture, probably for union with the palatine bone, while the rest of the 

 interior margin is free. It is removed some distance from the tooth-line 

 in consequence of the horizontal expanse of the bone, while the outer 

 face is vertical. 



The teeth are rod-like, the upper portion subcylindric in section, with 

 the inner face flattened from apex to base, while the lower half is flattened 

 externally by an abrupt excavation to the middle for the accommodation 

 of the crown of the successional tooth. The inner face of the tooth, from 

 apex to base, is shielded by a i^late of enamel, which is somewhat ele- 

 vated at the margins, and supports a keel in the middle, thus giving rise 

 to two shallow longitudinal troughs. The remainder of the tooth is 

 covered with a layer of some dense substance, possibl^^cementum, which 

 overlaps the vanishing margins of the enamel. The outer inferior exca- 

 vation of the shaft presents a median longitudinal groove, to accommo- 

 date the keel of the closely-appressed crown of tie successional tooth. 

 The apex of the tooth being obtusely wedge-shaped, the functional tooth 

 is pushed dosvhward and transversely toward the inner side of the jaw. 

 The tooth slides downward in a closely-fitting vertical groove of the 

 outer alveolar wall. The inner wall is oblique, its section forming, with 

 that of the outer, a V ; it is furrowed with grooves similar and oppo- 

 site to those of the outer wall, but entirely disconnected from them. 

 The base of the shank of the functional tooth, on being displaced by the 

 successional, slides downward and inward along the groove of the inner 

 side, each lateral movement being accompanied by a corresponding pro- 

 trusion. At the most, three teeth form a transverse line, namely, one 

 new apex external, one half- worn crown median, and the stump or 

 basis of a shank on the inner. The new crowns are, however, protruded 

 successively in series of three, in the longitudinal direction also. Thus, 

 when an apex is freshly protruded, the shank in front of it is a little 

 more prominent, and the third stands beyond the alveolar border. As 

 each shank increases somewhat in diameter downward in the C. arc- 

 tatus. the section increases in size with protrusion ; hence, before the 



