188 PALEONTOLOGY OF ILLINOIS. 



afforded Mr. Van Home three individuals, one of which is doubt- 

 ful, the others representing the forms identified with the posterior 

 teeth of the upper and lower jaws. There are also a couple of 

 similar specimens from the same horizon, one from Monroe county 

 and the other was found by Master Willis Worthen at Golden 

 Bluffs, near Warsaw, in this State. From Indiana localities, proba- 

 bly on equivalent strata, we have seen similar teeth, but these are 

 not now accessible to us for critical comparison. 



With a single exception, all of the above mentioned specimens 

 are too imperfect to allow of satisfactory definition and comparison 

 with the species known from other formations, hence we hesitate to 

 undertake their discrimination from allied species which they closely 

 resemble, occurring in earlier and later formations. The small im- 

 mature individuals of Sandalodus hevissimus, of the Keokuk lime- 

 stone, offer in a general way many features in common with their 

 Warsaw representatives ; while the Upper Burlington species, S. com- 

 planatus, especially the excessively arched examples of the mandi- 

 bular posterior form, strikingly resemble certain individuals occurring 

 in the Warsaw beds. On the other hand, the latter deposits afford 

 specimens of the same form which might readily be identified with 

 that belonging to S. spatulatus of the succeeding St. Louis forma- 

 tion. We are well aware how deceptive are the characters afforded 

 by imperfect materials in this group of fossil teeth, especially when 

 they are not supplemented by a large number of examples from which 

 a more comprehensive understanding of the specific characteristics 

 may be derived. And so far as relates to the specimens here par- 

 ticularly alluded to, we can only reiterate the facts relating to their 

 resemblances, leaving those that may be regarded as peculiar and 

 indicating specific distinctness for future amplification and demon- 

 stration. 



Geological position and localities : Warsaw limestone, Warsaw; Piasa 

 creek above Alton, and Monroe Co., 111. 



SANDALODUS SPATULATUS, N. and W. 



PI. XII. Fig. 7. 



Sandalodus spatulatus, NEWBEBBY and WOKTHEN, 1866, 111. Geol. Surv., II, p. 103, PI. X, f. 2. 



Deltodus rhomboideus, NEWBEBBY and WOETHEN, 1866, ib., II., p. 100, PI. IX, f. 8. 



Sandalodus crassus, NEWBEEEY and WOETHEN. 1870, ib., IV, p,3C9, PL IV, f. 3. 



Mandibular median teeth small, trapezoidal in outline, moderately 

 arched in the direction of inrollment, breadth apparently exceeding 



