338 PALJ30NT0L0QY OF ILLINOIS. 



nal fold exceedingly delicate striae. Base narrower and thinner than 

 the crown, relatively deep, and produced posteriorly slightly oblique to 

 the vertical "plane of the crown, rectaugular in outline, posterior face 

 slightly convex, anterior face of less depth, moderately excavated, with 

 a narrow shoulder parallel with and just beneath the coronal border, 

 which is produced into a more or less conspicuous basal protuberance 

 corresponding to the median angulation in base of the coronal region, 

 inferior surface well-defined, very obliquely beveled to the posterior 

 edge ; basal surfaces more or less coarsely roughened or pitted. 



Many specimens present the teeth in serial order, in which condition 

 they are sometimes soldered at the impingement of their bases into a 

 common basal support, the inrollment of which strikingly recalls the 

 form of the large triturating plates of Psephodus; again, in other series, 

 each tooth is distinctly separated by suture from the contiguous teeth, 

 and in isolated specimens the basal portion is entire, proving that till 

 the teeth were not intimately associated by the co-ossification of their 

 bases. 



From the general figure of these series of teeth, it is difficult to avoid 

 the use of the same descriptive phraseology employed in defining the 

 outline and contour of the large iurolled crushing teeth of the Gochlio- 

 donts. Whether the small apical or terminal teeth are defaced by the 

 effects .of attrition while in use, or that they have suffered abrasion 

 subsequent to their removal from the jaws, it is difficult to determine. 

 In the latter case these terminal teeth might appear to be the immature 

 inner teeth of the series; but we cannot overlook the fact that in most 

 of the Gochliodonts the apical extremity of the inrolled teeth was buried 

 in the integument of the jaw upon which they rested, and whether or 

 no they were so buried, they always present the imperfectly preserved 

 or abraded condition which is noticeable in connection with the lesser 

 teeth of the series of the present forms. Further, in all individuals of 

 Cochliodonts the coronal surface bordering the inner margin of the teeth 

 is usually without blemish, except in such as bear evidence of having 

 been beach-worn prior to their having been imbedded, and it is a note- 

 worthy fact that quite all the specimens of the species noticed under 

 the present genus present the large teeth of the series in a remarkably 

 perfect state of preservation. In view of these facts it is difficult to 

 resist the conclusion that these teeth constituted part of the dental 

 apparatus of a Cochliodont genus. On the development of the teeth 

 some of our material exhibits interesting data. In rare instances, and 

 in none better than in a specimen discovered by Mr. Van Hoene, series 

 show the innermost or newest formed tooth to be markedly less in size 

 than its immediate predecessor ; thus it would appear that the forma- 

 tive matrices do not at the outsetde termiue the full dimensions of the 



