54 IOWA STUDIES IN NATURAL HISTORY 
tained by Mr. Wilderboer, the collector for Sir Rawson Raw- 
son, after the latter had left Barbados, and having come into 
the hands of Alexander Agassiz, it was sent by him to Sir 
Wyville Thomson, together with the Holopus material obtained 
during the dredging expeditions of the ‘‘Blake.’’ This con- 
sisted of the very young individual dredged at Station 22, off 
Bahia Honda, Cuba, in 100 fathoms, and a single post-radial 
series dredged at Station 157, off Montserrat, in 120 fathoms. 
Carpenter noticed that the pentagonal figure indicating the 
position of the fuleral ridges on the articular faces of the ra- 
dials, and the central canals, can be traced almost to the bottom 
of the hollow cylinder forming the column. From analogy with 
other erinoids he believed that the small portion of the calyx 
tube between the limit of the pentagonal figure and the ends 
of the central canals and the spreading base consists of closely 
anchvlosed basals, the presence of which was taken for granted 
by Sir Wyville Thomson. He found that the calyx tube nar- 
rows rapidly downward, and its interior is marked by five ver- 
tical ridges corresponding with the radials in position. They 
are fairly distinct at the level of the section just above the 
portion formed by the supposed basals, but become less marked 
as they proceed downward, and, being composed of the whiter, 
less dense, network, disappear together with it. They extend 
upward to the edge of the cup at the intermuscular notches, 
although they are much less distinct on some of the radials than 
on the others. They thus oceupy the position of the ventral 
radial furrows which are often so marked on the interior of 
the calyx in other erinoids. 
Carpenter pointed out that on the bivial arms of the large 
specimen in the collection of the Museum of Comparative 
Zoology (No. 5 in the appended list of known specimens; Cat. 
No. 21, M.C.Z.) there are two primibrachs which look as if they 
were articulated rather than suturally united, while on the tri- 
vial arms there is only one. He believes that the evidence is 
sufficient to bear out the statement that Holopus has two primi- 
brachs which are closely united by syzygy; he says that we 
should accordingly expect to find a similar syzygial union be- 
tween the first and second brachials, but that of this there is 
no evidence whatever. He notes the complete absence of syzy- 
gies in the arms. 
