VEBTEBBATES. 315 



Generically considered, the teeth present closest affinities to Orodm, 

 Ag, a group prevalent in the Lower Carboniferous formations. But 

 the present group of teeth is distinguished by the prevailing promi- 

 nence of the buttressed condition of the anterior coronal borders, and 

 the relative uniformity or evenness of the posterior face, besides the 

 relatively fewer rows of acuminate teeth, as inferred from this feature 

 being so prevalent in all collections of Orodi, while the linear forms 

 are least commonly met with. The teeth of the extreme anterior rows 

 present the most marked divergence from the normal features just allu- 

 ded to, assuming a more or less circular outline as seen from above, 

 sometimes with the anterior face produced into a single more or less 

 prominent buttress. The latter feature may be readdy explained by 

 examining the tooth figured PI. S, fig. 15, in which the extremity of a 

 small linear tooth shows a tendency to throw off a pair of minute inde- 

 pendent teeth whose anterior angulation correspond to the buttresses 

 in the other portion of the crown. The variety assumed by the teeth of 

 the extreme rows of the jaw, as they occur in at least one specific form, 

 is partially shown in the figures PI. S, fig. 15-20 ; of these, 15-17 pro- 

 bably belonged to the maxillaries, 18-20 to the mandibles. The basal 

 portion of the teeth would seem to partake to greater or less extent in 

 the variableness observed in the coronal region : the normal teeth 

 presenting a quite persistent uniformity in general outline and propor- 

 tions, being more or less compressed antero-posteriorly and obliquely 

 produced downward and backward, vertically arched below with a more 

 or less prominent transverse ridge beneath the coronal border, extremi- 

 ties angular, one or other (probably the anterior) more produced late- 

 rally ; anterior face vertically concave, interrupted along the upper 

 borders by the supports of the coronal buttresses which originate in 

 the basal surface ; inferior surface well defined, flattened nearly in the 

 same plane as the crown, with which it agrees in proportionate outline, 

 though relatively narrower antero-posteriorly, plane or faintly chan- 

 neled, smooth or obliquely striated, the stria? or ridges being directed 

 from the inner margin obliquely-forward to the outer edge; either face 

 of the base more or less deeply and irregularly pitted. The coronal 

 region is enveloped in an enamel-like layer, and which is almost univer- 

 sally of a light color, often a lustrous white, producing a marked con- 

 trast to the black basal portion of the tooth, only rare examples obtained 

 from pyritose shales having a uniform black color. In the details of 

 coronal ornamentation, as well as those persistent proportional features, 

 the various specific forms are recognized. 



Besides the teeth, there remain to be mentioned some peculiar little 

 bodies which are intermingled in the mass of shale in which the teeth 

 were imbedded, with fragments of the cartilages of the skeletal frame, 



