2S4 PALAEONTOLOGY OF ILLINOIS. 



This species will be distinguished, at a glance, from the last, by its much 

 shorter and more gibbous form, and coarser concentric striae, as well as by its 

 angular, posterior, unibonal slopes. As we know nothing of its hinge or inte- 

 rior, it is only placed provisionally in this genus. 



Locality and position : Same as last. 



GASTEROPODA. 



Genus DENTALIUM, Linnaeus, 1758. 



(Syst. Nat. Ed., 10, p. 785.) 



Dentalium venustum, M. and W. 



PL 19, fig. 8. 



Dentalium venustum, Meek and Worthen, June, 1861. Proceed. Acad. Nat. Sci., Phil- 

 adelphia, p. 145. 



Shell very slender and slightly tapering, nearly straight, 

 rather thin; section circular; surface smooth. Length, 0.80 

 inch ; diameter of larger end, 0.09 inch; do., at smaller end, 

 0.03 inch. 



It is probable that where the surface of this shell is well preserved very fine 

 strife of growth could be seen by the aid of a lens, but in all of those we have 

 examined, no traces of surface markings of any kind are visible. It seems to 

 be allied to D. antiquum, of Goldfuss (a Devonian species), but is proportion- 

 ally thinner, and has a smoother surface. From D. priscum, of Munster, it 

 differs in being much more slender, and more gradually tapering. 



We have before us a few fragments of apparently the same species, but of 

 larger size, from Spergen Hill, Indiana, where they were found associated with 

 the small fossils described by Prof. Hall, from that locality. 



Prof. Hall has described, in the Iowa Report, p. 666, a larger, more robust, 

 and more curved species, from Warsaw, Illinois, under the name of D. prima- 

 riitm, and gives the Warsaw limestone as its geological position. This, however, 

 is an error, the specimen described by him belongs to one of us (A. H. 

 W.), and is from the Keokuk group, at Warsaw. 



Locality and position : Same as preceding. 



