18S7.] NATURAL SCIENCES OF PHILADELPHIA. 91 



the spiracles." They "have little doubt that this is fundamentally 

 the same structure as was seen by both Shumard and Hambach." 

 According to the latter author, there are "about five" of the sup- 

 posed tubes to each spiracle ; while Shumard says that two series of 

 pieces stand over each opening, and except in the anal interradius 

 this seems to be the condition of Mr. Wachsmuth's specimen also. 

 But we do not think that the pieces have the tubular nature which 

 Hambach assigns to them ; for we doubt whether they are more 

 than the proximal pinnules grouped around the peristome as shown 

 in our PI. V, fig. 28." 



In their explanation of the plate, this figure is said to be a "ra- 

 dial view of a decorticated specimen, with the pinnules rising above 

 into a kind of dome." No allusion is made to any difference be- 

 tween the bundles of jointed pinnules which fall over the summit 

 from each side, and the set of apparently rigid, erect and jointless 

 appendages which are seen between them. Nor do the authors any- 

 where in the text appear to recognize any such difference, although 

 it is to us quite apparent, both in the figure and in the specimen 

 which was before them. 



After arriving at this as a probable interpretation of the struct- 

 ures observed by Shumard and Hambach and figured by themselves, 

 and dissenting /rom Hambach's supposition, that the so-called tubes 

 pass down into the interior of the calyx, they arrive at this further 

 conclusion : "We are much more inclined to think that we have 

 here to deal with an extension of the smaller system of summit 

 plates, which occur in other Blastoids. In Granatocrinus and Elae- 

 acrinus only the peristome appears to be covered, (PI. VII, figs, 4. 

 11. 13 ; PI. XVIII, fig. 16), except perhaps for the anal aperture in 

 G. Norwoodi; while Orophocri7ius and Stephanocrimis have a gronip 

 of plates around the anal aperture (PL XIX, fig. 9). In Peutre- 

 mites conoideus the other four spiracles are perhaps also closed by 

 plates ; and except in the larger size and abundance of the plates it 

 is no o-reat advance from this condition to that which we have seen 

 in Pentremites sulcatus (PI. I, fig. 8.), but we await further informa- 

 tion." 



The supposed closure of the spiracles by plates in Pentremites 

 conoideus proves to be unsupported by the facts. A correct under- 

 standing of the nature of the pyramid surmounting the vault in 

 Pentremites sulcatus and allied species will, we think, fully demon- 

 strate that this structure, which probably existed in all Pentremites, 

 is a totallv different thing from the covering of the anus in Orojiho- 



