36 



Trans. Acad. Sci. of St. Louis. 



externally in the adult species, and in others they are never 

 visible externally. Ambulacrum rather broad. Column 

 round. 



This genus will include the following species : — 



1. Pentremites abbreviatus, Hambach, 1880. Chester 

 limestone. 



This species is erroneously taken to be identical with 

 Pentremites godoiii, by Etheridge, Jr., and P. H. Car- 

 penter, C. E. Keyes, and others. In so doing they mis- 

 take the facts, and I must say that none of these 

 gentlemen is acquainted with this species. If they 

 were, or if they had taken the trouble to compare my 

 figure and description* with Pentremites godoni, they 

 would have seen that they are not one and the same 

 species. Carpenter's figuref does not represent the 

 essential characters given in my description, which 

 makes it differ from the typical Pentremites godoni. 

 My species is quite rare, and has, as far as I know, 

 been found only at one small locality, about 500 feet 

 square, in a semi-oolitic limestone, although the whole 

 country around is rich in Pentre^nites, especially in 

 Pentremites sulcatus. The specimen figured by me 



is the largest I have 

 ever seen of this spe- 

 cies. In all specimens, 

 whether lara-e or small, 

 the transverse diameter 

 is ^ larger than the 

 vertical one. The in- 

 terambulacral space is 

 more rounded, also the 

 ambulacrum, and there 

 is not a sharp crest at 

 both sides of it as we. find in Pentremites godoni. 



Fig. 12. 



b. 



Pentremites abbreviatus. 



" godoni. 



" florealis. 



* Transactions St. Louis Academy of Science, Vol. IV., p. 155, Fig. 3. 

 t Catalogue of the Blastoidea, Plate II., Fig. 4. 



