Pores in Fistulatc Crinoids. — Springer. 147 
{ound them to penetrate the sac to a connec-tion with the inner 
cavity, just as those shown by these figures. We should of 
course not expect to find a greater number of pores exposed 
by one cross-section, as they are not arranged in transverse 
h'nes. The pores in this species are not found on every side 
of every plate in the sac, but they are very numerous, and 
whenever they occur, it is in the invariable position above de- 
scribed. 
Seaphiocrimis arborens VVorthen. PI. XVI, figs. 18, 19, 
20, 21 22 2'\. 
Although the foregoing examples, especially the last one, 
would seem to be sufificient for the present purpose, I will, 
for still further assurance, offer a study upon one more 
species, of which I have material in such preservation and 
abundance as to afford the best means of all for demonstrat- 
ing the nature of the structures in question. This is Seaphio- 
crimis arboretis, from the St. Louis limestone at Huntsville, 
Alabama, where it has been found in considerable numbers-. 
It is a small species, of the type of Seaph. unicus from the older 
Keokuk limestone, and is apparently its direct descendant. 
Its sac has the same peculiar crest of large plates, which are 
here only tumid, or very slightly spiniferous, and the anal 
opening is about half way down on the anterior side. The 
main portion of the sac below the crest, instead of having 
the profuse stellate ornamentation of 5. unicus, is in most 
of the specimens nearly smooth. In some few places the 
stellate ridges are obscurely indicated. Out of a considerable 
number of specimens disclosing portions of the ventral sac, 
I have about twenty-five in which the pores are plainly vis- 
ible in various parts of the sac. The sacs are in almost all 
positions, and in some cases the plates are well ^separated, 
so that the edges can be seen. The substance of the fossils is 
an exceedingly fine grained carbonate of lime, somewhat sil- 
icified, and of a rather light gray color. The matrix is an 
equally fine grained silicious limestone, of darker color than 
the fossils. x\ll the cavities, being filled up by the infiltration 
of this fine material, show darker than the test. Wherever 
pores exist they are perfectly visible, and in some places the 
infiltrating material has been dissolved out again, leaving the 
