4 



profusion of Gasteropods, and also the worn character of 

 many of the shells, induces me to conclude that the water 

 of the ancient sea was extremely shallow at this place. It 

 is likewise upon the present eastern margin of the Carbon- 

 iferous limestones, and we have many reasons for believing 

 that this primeval ocean never extended much farther east 

 than the present limits of the limestone. 



My attention has been especially called to these fossils dur- 

 ing the past year, by Mr. H. C. Grosvenor, of Cincinnati, 

 who has made several collections at Spergen Hill, and to 

 whose kindness I am indebted for a complete suit of speci- 

 mens from this locality. Mr. Worthen has also made col- 

 lections of the same for me at Bloomington, Indiana, and 

 from above Alton, Illinois. 



The numerous species common to several widely sepa- 

 rated localities seem sufficient evidence to warrant us in 

 placing the beds of all these places in the same horizon. 



The descriptions of several species of Bryozoa which oc- 

 cur with these fossils have been postponed for the present ; 

 but I have little doubt of being able to present evidence, 

 from these fossils alone, of the identity of the Spergen Hill, 

 Bloomington and Alton beds, with the Warsaw Archimedes 

 limestone. 



PENTREMITES, Say. 



^Pexteemites Koxixckaxa. — Small, globose, or subpyri 

 fornijUpper part rounded, base sub-pyramidal, angular ; basal 

 plates small, the lateral edges short and covered by the col- 

 umn, allowing the base of three of the radial plates to come 

 within the limits of the column area, the two other plates 

 resting upon the longer sides of the larger basal plates. 

 Radial plates short, convex in the middle and sloping to 

 the sides, widening a little from the base upwards, and di- 

 vided only half way down for the reception of the pseudo- 

 ambulacral areas ; interradial plates minute, linear or taper- 

 ing very gradually upwards to a point, and having two ex- 



