56 IOWA STUDIES IN NATURAL HISTORY 
eighteen small distal brachials, raising the total number of 
brachials to between twenty-five and thirty. 
The longer outer sides of all the brachials bear the pinnules. 
That of the first brachial is comparatively small, and is at- 
tached close to the distal edge of the segment; the next pinnule 
is invisible in all the specimens, but those of the third and 
following brachials are much larger and have broad basal seg- 
ments that gradually come to occupy more and more of the 
whole surface of the brachials to which they are attached; in 
fact the bases of the pinnules of alternate brachials that are 
borne upon the same side of the arm are only just separated 
from one another by the narrow ends of the intervening bra- 
chials which have their pinnules on the opposite side. The 
pinnules are rolled in upon themselves in exactly the same way 
that the arms are. The four or five basal segments are very 
broad, but the rest of the pinnule tapers away rather rapidly. 
The segments are united by paired muscular bundles, which is 
a somewhat unusual condition. 
The central mouth is protected by five large and triangular 
oral plates which are opposite the clavicular pieces of the united 
radials. The lateral edges of these plates are more or less cut 
into false teeth, while the raised central portion is pierced by 
from fifteen to twenty minute holes, the water pores. The bases 
of the orals seem sometimes to rest directly against the edge of 
the radials, while they are sometimes separated from this edge 
by an irregular row of small triangular plates. Carpenter says 
it is not unlikely that an anal tube is concealed somewhere or 
other among these plates, but he saw no certain traces of it in 
the dry specimen. 
The food grooves which come away from the mouth between 
every two of the oral plates are continued out upon the axil- 
laries and thence on to the arms. They occupy the deep chan- 
nel between the large muscular processes at the sides of the 
segments, and in the dry specimen appear to be bordered by 
small irregular plates. These, however, do not seem to corres- 
pond either to the side plates or to the covering plates of other 
crinoids, for an examination. of the spirit specimen shows that 
these small plates really belong to the tentacles, which are rela- 
tively large and stout. The bases of these tentacles are pro- 
