16 Trans. Acad. Sci. of St. Louis. 



remain there, which also accounts for the irregularity of 

 these coverings as described and figured by the different 

 authors. It is strange that every one adheres to the old idea 

 of Shumard, and that no one has taken the pains to examine 

 the matter more carefully in order to convince himself of the 

 true nature of it. This irregular arrangement of the pieces 

 covering the summit openings, as described by Eastman,* is 

 evidence for the contradiction of his statement, because it 

 is hard to suppose that specimens belonging to one and the 

 same species should not have a uniform arrangement in the 

 covering plates of their openings if such a covering existed. 



It is true that Wachsmuth admits, after seeing Shumard' s 

 type specimen of Pentremites conoideus that the summit 

 openings are not closed in the manner described by Shumard 

 but he still believes that they are closed. 



It stands to reason and is only logical to suppose that, if 

 nature provided an opening it should remain open or that the 

 covering is a flexible one and not formed by additional plates 

 inserted into the openings as intimated by all authors who 

 adopted the first statement of Shumard. No one explains or 

 gives any reason w^hy the opening should be closed. Every 

 one disregards the fact that all casts of the interior of a calyx 

 exhibit on the summit a cast of the summit opening, which 

 could not be possible if the openings had been closed by ad- 

 ditional pieces. This fact has not been observed on speci- 

 mens of Olivanites or others where the center of the summit 

 is closed. 



THE WATER VASCULAR SYSTEM. 



On the under side of the lancet piece and completely 

 filling the semi-lunar groove we find a tubular vessel con- 

 necting with a circular ring underlying the base of the 

 deltoid and surrounding the central orifice. The thickness 

 of this vascular ring and its branches varies according 

 to the species. The diameter of this vessel is about 

 1-20 of an inch in a large specimen of Pentremites sulcatus. 



* Text Book of Palaeontology, Vol. I., p. 197. 



