144 PALEONTOLOGY OF ILLINOIS. 



although in outline and general appearance they are so markedly 

 different one from the other. A comparison of the forms reveals 

 the same depressed or sulcated anterior slope of the principal 

 coronal prominence, very oblique anterior portion of the inner mar- 

 gin and its abrupt deflection in passing around the base of the coro- 

 nal ridge into the posterior extremity ; even the articular edge of the 

 anterior borders in the two forms is very like, but in the postero- 

 lateral borders there is marked dissimilarity between them, nor have 

 we been able to identify amongst the material before us forms with 

 which the maxillary posterior teeth were associated. Whether the 

 upper jaw was terminated by a series of teeth, such as undoubtedly 

 occupied the anterior portion of the jaw in Cochliodus, it is impos- 

 sible at the present time to more than conjecture. 



The genus is represented by species thus far authentically reported 

 only in lower Carboniferous formations in Europe, where it was the 

 cotemporary of Cochliodus. In America, however, its representatives 

 range from near the base of the lower Carboniferous (Burlington 

 limestone), thence through the successive formations up into the 

 Coal Measures. The following is a list of the species at the present 

 time known, the affinities of the forms being recognized in accord- 

 ance with the characteristics cited in the foregoing descriptions and 

 observations : 



Deltodus sublcevis, Agass., mountain limestone, Great Britain. 

 ( Pcedlodus parallelus, McCoy, and possibly Poscilodus aliformis, Mc- 

 Coy.) 



D. sandalinus, de Koninck, Carboniferous limestone, Belgium. 



D. spatulatus, N. and W., U. Burlington limestone. 



D. occidcntalis, (Leidy sp.) Keokuk limestone. ( D. stellatus, N. 

 and W.) 



D. undulatus, N. and W. Keokuk limestone. 



D. latior, St. J. and W. Keokuk limestone. 



D. Littoni, N. and W. Warsaw limestone? 



D. cinctidus, St. J. and W. Warsaw limestone. 



D. trilobus, St. J. and W. Warsaw limestone. 



D. parvus, St. J. and W. St. Louis limestone. 



D. intermedius, St. J. and W. St. Louis limestone. 



D. cingulatus, N. and W. Chester limestone. 



D. Mercurii, Newb. Lower Carboniferous. 



D. Powellii, St. J. and W. Upper Carboniferous. 



D. propinquus, St. J. and W. Coal Measures. 



