146 Tlic American Geologist. September, 1900 
somewhat enlarged, in which the sac is exposed. The sac. 
especially in the lower part, is covered by a very sharp and 
prominent stellate ornamentation, composed of conspicuous 
ridges running from the middle of each plate to the angles, 
and there connecting with corresponding ridges on adjacent 
plates. This stellate surface arrangement, although most pro- 
nounced in the lower part, is quite plain up to the distal end. 
Throughout the exposed parts of the sac there are distinct 
and well formed pores, which are without exception located 
on the radial lines, at the middle of the sides of the hexagonal 
plates. They are on the sutures in the depressed portion of 
the plates, between the ridges. The arrangement of the pores 
and ridges is more plainly shown by figure 2, w-hich gives an 
enlarged view — 4 diameters- — of one of the plates with its con- 
nections. 
In order to determine the question whether these pores 
are mere surface ornamentation, or actual openings through 
the test, I have taken a portion of the ventral sac of another 
specimen, and ground off all projections upon the sur- 
face until it is perfectly smooth, and have also ground down 
the fractured end so as to obtain a transverse section. The 
results of these operations are shown by figures 3 and 4. Fig. 
3 is the polished outer surface, disclosing the sutures between 
the plates, and the pores on the sutures at the middle of the 
sides. The plates are rather irregularly hexagonal, and 
though perfectly smoothed off, preserve to some extent their 
stellate outline. The pores are not of uniform size or shape, 
but their position is the same throughout, viz.. at the middle 
of the sides. Fig. 4 is" the cross-section at the upper end of 
fig. 3; the inner cavity of the flattened tubular sac is plainly 
shown by the dark substance with which it has been filled 
by infiltration. The section cuts two of the pores, one large 
and one small one, which are seen at the upper edge of fig. 3. 
These are shown in the cross-section to pass from the ex- 
terior directly through the plates and connect with the inner 
cavity, being filled by the same kind of darker infiltrating sub- 
stance. The connection of these pores in the two views is 
shown by the dotted lines. In preparing this specimen I 
ground off the cross-section for a considerable distance, and 
in doingf so encountered several pores, and in every case I 
