G4 . PALAEONTOLOGY OF ILLINOIS. 



fine, but distinct, horizontal lines or folds. On the opposite 

 surface these are nearly obsolete. 



This slender and highly ornamented species, though presenting a general 

 similarity to several of the preceding group, may be at once distinguished from 

 them by the numerous fine horizontal lines which cover one face of the crown. 



Figure 5, 5 a, side view of a broken specimen, twice the natural size. 



Formation and locality : St. Louis limestone, St. Louis, Missouri. 



Oeodus elegantulus, N. and W. 



PI. IV, Figs. 6, 6 a. 



Teeth small, laterally elongated, narrow and slender; crown 

 conical, bearing a prominent central cone, from which the out- 

 line slopes away to either extremity. The median cone is 

 faintly marked with a few delicate radiating raised lines. On 

 either side of this are six or eight small tubercular secondary 

 cones, from each of which spring about three raised lines, 

 which diverge and cover most of the anterior face of the crown; 

 this line of prominent points is not medial, but nearer the pos- 

 terior than anterior border. The posterior face of the crown is 

 somewhat roughened with short, tortuous, raised lines and 

 tubercles. The crown is covered with a coating of dense trans- 

 lucent enamel, highly polished, and without pores. The root 

 seems to have been cartilaginous, and has usually disappeared. 



This eiegant little species bears considerable resemblance to the last, but is 

 somewhat larger and much smoother; the raised lines which ornament the sur- 

 face of the crown being comparatively few and faint, and having a different 

 arrangement. When seen on profile it exhibits some resemblance to 0. cinctus, 

 Ag., but on close examination it will be seen that the ornamentation is quite 

 different. In 0. ductus the median cone, as well as all the lateral prominences, 

 are unbroken rings which arch over from the front to the rear, while in our 

 species the central elevation is distinctly, sometimes acutely, conical, marked 

 with- radiating lines. The secondary tubercles are round, smooth, and distinct, 

 and from these, three or four sharp, raised lines, diverge to cover one side only 

 of the crown, constituting a much more complex and beautiful style of orna- 

 mentation. 



