229 



PALEONTOLOGY OF ILLINOIS. 



upon the jaws, we have yet to ascertain the relative disposition of 

 the individual teeth thereupon. The peculiar character of the inner 

 articular border permits of coadaptation neither with opposites of 

 the same form, nor with the other forms with the remains of which 

 the present one is associated, and we are left in doubt even as to 

 the generic identity of the latter. The crescent-shaped outline of the 

 inner articular faces indicate a corresponding convexity for the outer 

 border of the teeth of the contiguous row articulating with this 

 form. The space intervening between opposite individuals of the 

 form is lingulate in shape, but whether it was occupied by a single 

 row of lingulate teeth, or that these were further subdivided can 

 only be conjectured. On the other hand, if the dental formula 

 ascribed to the Upper Burlington species, P. Springeri, which seems 

 to be well founded, attributing to it a simple biserial arrangement, 

 be regarded as typical of the genus, then we should have in the 

 present form a new element further complicating the dental formula 

 to an extent which, if met with in existing Myliodonts, might con- 

 stitute a distinctive feature of generic significance. We are, how- 

 ever, fully cognizant of the meagerness of the data at this time 



possessed, and would clearly discrim- 

 inate between the facts themselves 

 and that which they suggest with 

 greater or less degree of plausibility. 

 The accompanying diagram repre- 

 sents the simplest dental combina- 

 tion of the form here particularly 

 alluded to. The lingulate teeth of 

 the median row certainly offer strong 

 resemblance to some of the generic 

 forms with which Copodus cornutus, 

 Agass., is associated ; but none such 

 have been recognized in the present 

 case. True, we have a form occur- 

 ring in the same horizon with the 

 present species which is referable to 

 the latter group ; but it clearly has 

 no intimate relationship with the 

 form in question. 



The few individuals mentioned 

 Psammodus crassidens. above as comprising the sole repre- 



