330 PALAEONTOLOGY OF ILLINOIS. 



STEM31AT0DTTS CHEIRIPORMIS. 

 PI. 8, Kg. 30 a,b,o. 



Under this term is included the form represented in tbe above referred 

 to illustrations, teeth which exhibit the extreme development of coronal 

 cusps, of which there are from three to four rows — the outline, as pre- 

 viously stated, being triangular, with one or other of the lateral margins 

 considerably more extended than the opposite side, thus producing an 

 unsymmetrical figure suggestive of the lateral position of the tooth or 

 its association with one or more companion teeth. The basal portion 

 has already been described; it deserves mention, however, that this 

 portion of the tooth, as shown in the several specimens, is more or less 

 modified by accidental causes, so that none of the specimens may 

 exhibit a perfect individual in this respect. But in the coronal region, 

 save what is due to attrition while the teeth were in use, there is quite 

 persistent uniformity in the number and disposition of the cusps and 

 rows. A specimen of medium size, as that figured, shows seven cusps 

 in the longer marginal row, five in the shorter or opposite row, and six 

 in the median row. In all these specimens the first three or four cusps 

 of each respective row in the anterior portion of the crown, seemingly 

 present a disproportionately small size as compared with those in the 

 posterior portions of the tooth ; but this may be attributable, in part at 

 least, to abrasion by which the anterior cusps have been reduced in 

 size, appearing as mere tuberculose prominences. In the larger and 

 more perfect posterior cusps, the form is moderately compressed antero- 

 posteriorly, rapidly tapering to the acutely rounded apex, the lateral 

 angles sharp, and both faces marked with numerous, sharp vertical 

 costae, those in the posterior face being relatively finer. In the majority 

 of specimens, perhaps, not a vestige of the coronal ornamentation 

 remains, and in some examples the cusps are so worn down throughout 

 as to give to the crown a striking resemblance to the teeth of Ctenodus, 

 which they also recall in shape. The specimen shown in fig. 29, PI. 8, 

 is probably a very eccentrically developed tooth referable to the present 

 form. 



STEMMATODXJS B1FTJRCATTJS. 



PI. 8, Fig. 31 a,l),c. 



The singular form here indicated is represented by a unique speci- 

 men. In shape it is like that above described, possessing three rows of 

 coronal cusps in the anterior half, but the median row suddenly termi- 

 nates with the fifth cusp, the two lateral rows being continued poste- 

 riorly in independent rami, bearing respectively eight and nine cusps, 



