38 Trans. Acad. Sci. of St. Louis. 



Shumard and many later authors confound this 

 species with Pentremites godoni, which is a sad mis- 

 take because there is a considerable difference between 

 these two species. In the typical P. florealis the body 

 is more elongated, the base portion drawn out and 

 more prolonged than in Pentremites godoni, and the 

 plications of the ambulacral integument are coarser 

 than in P. godoni. The typical Pentremites florealis 

 is comparatively rare in Alabama and Kentuck}^ but 

 not 80 at Chester, Illinois, where Pentremites godoni 

 does not occur at all. We find it again at Waterloo, 

 Illinois, associated with Pentremites florealis, but it is 

 by far the predominating species here. 



14. Pentremites gemmiformis, Hambach, 1884. Chester 



limestone. 



15. Pentremites godoni, De France, 1818. Chester lime- 



stone. 

 Kentucky arterial fossil, Parkinson, 1808. 

 Pentremites globosus, Troost. 



16. Pentremites hemisphericus, Hambach 1880. Chester 



limestone. 



17. Pentremites nodosus, Hambach 1880. Chester lime 



stone. 



18. Pentremites obesus, Lyon, 1857. Chester limestone. 



19. Pentremites pyriformis, Say, 1825. Chester limestone. 

 Pentremites subconoideus, Meek, a young form of pyriformis. 



This species differs from P. florealis, its nearest 

 relative, in having its greatest diameter at the apex of 

 the ambulacrum, dividing the calyx in two equal halves, 

 i. e., the distance from the articulation surface of the 

 column equals the distance from the apex of the 

 ambulacrum to the summit. 



20. Pentremites spinosus, Hambach, 1880. Chester lime- 



stone. 



