YEETEBEATES. 319 



sloping crest line, though they are nearly vertical to the general hori- 

 zontal plane of the tooth. The base presents the same outline as the 

 crown, the comparatively thin lateral portions gradually expanding in 

 thickness and depth posteriorly, terminating in an obtusely rounded 

 angle behind, the inferior median portion being deeply channeled, the 

 vertical or transverse striae becoming oblique when extended into either 

 lateral prolongation. In the direction and contour of the anterior and 

 posterior faces of the base, as also the lateral portions of the inferior 

 surface, no essential differences are observed by which it might be dis- 

 tinguished from the prevailing individuals. But in the symmetrical 

 form of the tooth, as indicated not only in the coronal region, but also 

 in the conformation of the inferior basal surface, there would seem to be 

 strong evidence that there existed but a single row of these teeth and 

 that this row was confiued to the symphisis, the lateral wings resting 

 respectively upon either ramus. As no similar shaped teeth are present 

 in the mandibular specimen described at length above, it would seem 

 apparent that, in case the present form belongs to the above species, it 

 probably pertained to the upper jaw. 



On the position of the teeth upon the jaw, reference has already been 

 made in the foregoing description. It remains to note in general the 

 variability of the individual teeth, and to what extent it is dependent 

 npon the relative position they occupied upon the jaw. In the rami of 

 the lower jaw there occurs as many as eighteen rows of teeth, or eight 

 at least anterior and nine posterior to the large median row, which 

 latter possessed above twenty-five individual teeth, while the lateral 

 rows ranged from forty to fifty and more, the posterior rows apparently 

 possessing the larger number. The diminution in size consequently 

 from the inner to the outer teeth of a row is very gradual, and the evi- 

 dence afforded by the large, mature ramus from Kansas would seem to 

 indicate the persistency of the teeth to an extent far in excess of that 

 of the modern Cestracion, or even of the Liassic Hybodonts, the decidu- 

 ous character of which, however, affords but a faint idea of the number 

 of teeth shed from the jaws as compared with the comparatively small 

 number permanently in use and in process of development at the same 

 time upon the jaws. It is evident that both jaws of a mature fish 

 probably possessed at least two thousand to two thousand five hundred 

 teeth. ' It may be of some interest here to make some estimate of the 

 probable size attained by this species. The common Cestracion of 

 the Australian seas, one of the most nearly allied living representa- 

 tives of these Carboniferous JSelacia-ns, presents the most accessible data 

 upon which to base our calculation. Of the latter an individual thirty 

 inches in length from snout to the caudal extremity, possesses jaws 

 the mandibular portion of which are about four inches in length. 



