96 PALEONTOLOGY OF ILLINOIS. 



of their possessors. In some specimens, as that discovered by Mr. 

 Wachsmuth, the abraded anterior coronal region presents a coarse, 

 irregular punctate structure, characteristic of the vaso-dentine com- 

 posing the body of the teeth. In mature and much-worn teeth 

 where the enamel and outer subjacent layers have been removed by 

 the process of attrition a similar exposition of the coarse, tubular 

 structure is laid bare all round the inner and outer margins of the 

 tooth; in other examples the abrasion has been carried so far as to 

 produce a deep channeling of the surface of the posterior prominence 

 in the direction of the long, or transverse diameter of the tooth; 

 and in those that preserve the crown surface in a perfect state, the 

 enamel along the inner margin, through which the minute, pris- 

 matic structure is visible, shows distinct parallel incremental lines, 

 more or less sharply impressed, and even reaching well up over the 

 crown, producing an irregular, undulated surface, extending alike over 

 the posterior prominence and the anterior neck. In well-preserved 

 specimens the secondary lobe in front of the principal coronal prom- 

 inence is denned with absolute distinctness. The posterior angle 

 probably terminated in a more or less produced spur, the enamel 

 apparently forming a narrow fold enveloping the superior edge of 

 the antero-lateral border, similar to what obtains in corresponding 

 teeth of Cochliodus; however, in some specimens this border is slightly 

 raised into a low, obscurely-defined marginal ridge. 



The mandibular posterior teeth, also, exhibit much the same 

 superficial features due to the various conditions of usage and pre- 

 servation as enumerated in connection with the teeth of the opposite 

 jaw. The anterior plane-belt is usually merged into the median 

 prominence toward the outer margin, the result of wearing down 

 of the crown surface ; but toward the inner margin the coronal 

 contour is well, even sharply defined, the surface enveloped in a 

 layer of polished enamel. 



Geological position and localities: Keokuk limestone : Warsaw, Ham- 

 ilton, Nauvoo, and Henderson county, (Illinois) ; Keokuk, Danville, 

 Bentonsport, (Iowa) ; Booneville, (Missouri). 



DELTOPTYCHIUS VARSOVIENSIS, St. J. and W. 



PI. V. Fig. 14. 15. 



Mandibular posterior teeth trigonal in outline, apparently strongly 

 inrolled at the outer extremity, inner margin very oblique and 

 broadly rounded with slight sigmoidal curvature, postero- lateral bor- 



