76 POLYGONODON. — IIADROSAURUS. 



a third has its convexity two inches wide, and twenty-one lines high. The spinal 

 canal, preserved in two of the specimens, has a semi-circular form in transverse 

 section, and measures nine Imes wide, and six lines high at the entrance. 



POLrYGO]\ODOI¥. 



Polyg'onodon Tetus. 



Poli/gonodon vetus, Leidy, Proc. Acad. Nat. Sci., 1856, VIII, 221. 



Polygonodon rectus, Emmons, Report Nortt Carolina Geological Survey, 1858, 218, Fig. 37, A. ; Manual of Geology, 



1860, 208, Fig. 3. 

 Alossosaurus rectus, Emmons, North Carolina Geol. Surr., 1858, 218. 



The name of Polygonodon ivtus was founded on a remarkable specimen, consist- 

 ing of a shed tooth, from the Green-sand of Burlington County, New Jersey, from 

 whence it was obtained by Lewis T. Germain, and Avas loaned to me for examina- 

 tion by Prof. Cook. The specimen represented in Figs. 12, 13, Plate IX, consists 

 of a nearly entire crown, worn at the apex and along the anterior and posterior 

 borders. In construction it resembles the croAvn of the teeth of Mosasauriis, but is 

 exceedingly narrow in comparison. It is in the form of a slender cone with the 

 length more than three times the breadth of the base, compressed from without 

 inwardly, and slightly curved inward and backward. It is nearly equally divided 

 by acute ridges extending the length of the crown anteriorly and posteriorly. The 

 ridges are much worn, so that it cannot be ascertained whether they were denticu- 

 lated. The surfaces of the crown are subdivided into well-defined and 

 No. 34. slightly unequal narrow planes, there being seven externally and six in- 

 ternally. The enamel is quite smooth, though finely fissured longitudi- 

 nally and jet black in the specimen. The transverse section, as represented 

 in the outline, No. 34, is elliptical with acute poles. The base is hoUoAved 

 into a shallow funnel from a thick broken edge to a central pulp cavity, which is 

 small, narrow, and of the shape of the crown. The interior dentine is jet black 

 and of dense structure. 



The length of the specimen is twenty lines ; its width at base six lines by four 

 lines and a half. The tooth may have belonged to Discosaurus or CimoUasaurus, 

 but the matter must be left for future determination. 



A specimen, identical in form and size with that just described, was found by 

 Prof. Emmons on Cape Fear lli\er. North Carolina, and Avas probably derived from 

 the Green-sand. It is described and figured in the North Carolina Geological 

 Survey, page 218, Fig. 37 (A). 



HADROSAIJRUS. 



Iladrosauru!^ Foulkii. 



I/adrmaimis Foulkii, Leidy, Proc. Acad. Nat. Sci., Phila., 1858, 218. 



A remarkable reptile, of huge proportions, has been proved to have existed during 

 the C'retaceous period of the Western Continent, to which the name of Hadrosanrus 

 Foulliii has been applied. 



