BARBADOS-ANTIGUA REPORTS oT 
tected by scale-like plates formed of the usual calcareous reticu- 
lation; they are not easily made out at the edges of the bra- 
chial groove, but on the lower parts of the pinnules there seem 
to be from two to three tentacles on either side of each segment. 
The general arrangement of the tentacles is the same as in 
other crinoids, but the epithelial layer covering them is, if any- 
thing, thinner than in Heliometra glacialis, though thrown into 
much stronger corrugations at the ends of the tentacles. 
Carpenter found that cutting sections of a Holopus arm was 
an exceedingly difficult task, partly because of the rolled up 
condition, and partly because the calcareous substance of the 
skeleton is so much denser than that of other crinoids, so that 
the organic base which is interpenetrated by it and remains 
behind after decalcification has nothing like the consistency that 
we meet with in the corresponding parts of the comatulids or 
of Ilycrinus. The presence of large bundles of muscles and 
ligaments without any helping syzygies also increases the diffi- 
eulty of all attempts to obtain thin sections. 
He found that the anatomy of a Holopus arm is similar in 
all essential respects to that of an ordinary ecrinoid. The axial 
cord traversing the central canal of the skeleton gives off its 
pinnule branches in the usual way, that is, alternately on op- 
posite sides. These branches have a long distance to go before 
they reach the pinnules, owing to the attachment of the latter 
on the upper edges of the large muscle plates. As long as the 
branch remains in the substance of the brachial it does not take 
a straight course as is the case in the other erinoids, but is 
thrown into a series of loops in a dorsoventral direction, and 
aiter it enters the pinnule its course is still somewhat sinuous. 
These branches, like the main arm trunk, are relatively of very 
small size, which is perhaps to be accounted for by the fixed 
position of the animal. All the ambulacral structures of the 
TTolopus arm are lodged in the deep median groove of its skele- 
ton, and are usually small in comparison with the great trans- 
verse diameter of the ossicles. The cceliac canal is situated, as 
usual, between the two large muscle bundles, with a small genital 
eanal separating it from the single subtentacular canal above. 
The epithelial lining is very much the same in character in all 
these canals, consisting of low, flattened cells. In Holopus the 
