Geology. 



119 



ders. The inner surface of the tooth, presenting the five smaller sides of 

 the column, is quite roughened with irregular granulations. The base of 

 the tooth is hollow, and its walls at the broken border of the specimen 

 are 1-J lines thick. 



In another and much worn specimen of a tooth, which had apparently 

 been shed, and is now 4-J- lines long ; the triturating surface is slightly 

 concave and pentahedral, with concave sides, and is 4 lines in diameter. 

 The two portions of the outer surface incline much more from the median 

 ridge than in the preceding specimen ; and the base of the tooth is hol- 

 lowed, apparently from the pressure of a successor. 



(3.) Troodon formosus, Leidy. — The genus and species are founded on 

 a single specimen of a tooth of a lacertian, discovered by Dr. Hayden. 



The specimen consists of a compressed, curved, conical crown with 

 trenchant edges. The outer side is more convex than the inner, which is 

 worn off towards the apex from friction of the opposing tooth. The 

 trenchant edges are coarsely denticulated ; the denticulations themselves 

 being compressed conical, with trenchant edges, and are bent in such a 

 manner that their apices are directed towards the summit of the crown. 

 The base of the tooth is hollow, and is 2 lines wide and 1J lines trans- 

 versely ; and the length of the specimen is 3 lines. 



(4.) Deinodon horridus, Leidy. — This genus and species are founded 

 on a number of specimens, consisting of fragments of teeth of a saurian 

 reptile, discovered by Dr. Hayden. 



Nine of the specimens referred to consist of crowns of teeth or of their 

 summits, which resemble those of Megalosaurus, being compressed coni- 

 cal and curved, and having trenchant, dentated borders. They are gene- 

 rally thicker in relation to their breadth than in Megalosaurus, which 

 might only be a specific distinction, were it not that there are several 

 other teeth in the same collection apparently of the same animal, but 

 quite peculiar in form. 



One of the specimens is a curved conical crown, nearly circular in 

 transverse section, having a prominent dentated ridge on each side. A 

 second specimen is a crown, semi-elliptical in transverse section, with the 

 posterior borders dentated. A third specimen is a small fragment of a 

 very large tooth, apparently with nearly the same form as the latter ; and 

 a fourth specimen is a portion of the crown of a tooth, semi-elliptical in 

 transverse section, with the posterior borders elevated but not dentated. 



Had the different forms of teeth above indicated been obtained from 

 different localities, they might have been referred to at least four distinct 

 genera, but having been discovered together, and possessing the same 

 structural appearances, I suspect them to have belonged to one and the 

 same species. 



The largest specimen resembling the teeth of Megalosaurus in its pres- 

 ent condition, is 1\ inches long from the apex, §- of an inch broad at 

 base, and 5 lines thick. One of the specimens, which is semi-elliptical 

 in section, is over an inch in length from the apex, 8 lines broad at base, 

 and 3-J lines wide at the posterior surface. Another specimen, apparently 

 with the same form as that just indicated, in its perfect condition appears 

 to have had the crown over two inches in length, nearly an inch in 

 breadth, and about half an inch in width posteriorly. 



