168 PALAEONTOLOGY OF ILLINOIS. 



compared with the relatively thin antero-lateral edge, presenting a 

 deep, slightly channeled, inbeveled belt bordered above by the thick, 

 rounded enamel fold ; inner margin making an angle of about 30 with 

 the anterior articular border to the base of the coronal ridge, where it 

 is abruptly rounded and deflected nearly at right angle to its ante- 

 rior course with a slight concavity in passing the posterior depres- 

 sion to the subacute posterior angle. Coronal contour strongly 

 marked by the elevated ridge which culminates in a rounded crest 

 overhanging the deep, narrow posterior depression, the wide anterior 

 slope presenting a slight transverse concavity; posterior alation 

 forms a rounded lobe well denned from the groove-like posterior 

 depression. Surface showing more or less distinct longitudinal plicaB 

 in the less worn enamel layer toward the inner margin, and traversed 

 by transverse lines and faint undulations ; puncta? fine, crowded, 

 showing tendency to conform in their disposition to the transverse 

 lines. 



The collections afford only two examples of the above described 

 form, neither of which are sufficiently perfect to permit accurate 

 measurement of their dimensions, although sufficiently so to allow 

 satisfactory comparison with allied species. In size and general 

 outline it agrees with its predecessor, Deltodopsis ? convolutus, of the 

 Upper Burlington limestone, from which it is distinguished by its 

 appreciably more robust build, and especially by the overhanging 

 crest of the coronal ridge or the inflexed slope descending into the 

 narrow posterior depression, and the distinctly lobed condition of 

 the alation. 



Geological position and locality: Keokuk limestone ; Warsaw, Illi- 

 nois. 



DELTODOPSIS ? BXORNATUS, St. J. and W. 



PL XI. Fig. 14. 



Teeth small, subtrigonal in outline, strongly arched longitudinally, 

 and very strongly inrolled spirally. Antero-lateral border propor- 

 tionately short, basal portion channeled and bordered by the thick- 

 ened, inbeveled enamel fold ; postero-lateral border rapidly converging 

 toward outer inrolled margin ; inner margin, from the obtuse anterior 

 angle, very obliquely deflected backward in a slightly concave curva- 

 ture, abruptly rounded at the base of the coronal ridge, with a 

 shallow concavity thence to the posterior angle ; coronal ridge prom- 

 inent, the sharply rounded crest culminating nearest the postero- 



