52 IOWA STUDIES IN NATURAL HISTORY 
tubercles scattered over it. No trace of divisions ean be de- 
tected in this part. Above, there are two circles of five plates 
each, fitting closely together and concealing the arms entirely. 
The lower plates are pentagonal with rounded corners, the upper 
and lower sides being parallel. The lower sides do not form a 
continuous line from plate to plate, so that there are small 
triangular spaces left between. them. There is a row of tubercles 
on each side of a plate, and one in the middle forming a ridge 
which projects a little downward over the lower edge of the 
plate. On the upper edge of these plates are articulated five 
smaller triangular ones, firmly closed together. They have also 
a ridge in the middle in continuation of the ridge in the lower 
plates. The larger pentagonal plates are the radial axillaries 
of Sir Wyville Thomson, but the smaller triangular ones seem 
to become fused with them in the adult. Color black. Diameter 
at base 3 mm.; height a little over 1 mm.”’ 
I think it well here to observe in regard to this young speci- 
men that there is room for considerable doubt whether it be- 
longs to the genus Holopus. There are but five arms, forming 
a tightly closed pyramid, without any sign of an axillary plate 
such as should appear at any post-larval stage of Holopus; and 
the facets for the reception of the arm bases incline inward, 
instead of outward or horizontal as in typical specimens. In 
the latter respect it is more like the fossil genus Cyathidium, 
described in 1847 by the Danish author Steenstrup, from the 
upper chalk of Denmark; and also in the tightly closed pyramid, 
which has by the later discoveries of Brunnich Nielson’ been 
shown to be the condition of the arms in Cyathidiwm, which 
however has at least three axillary pieces. 
Dr. P. Herbert Carpenter in 1884° gave a very detailed ac- 
count of this genus. He defined the family Holopide as fol- 
lows: 
‘‘Basals and radials completely anchylosed into an asymmet- 
rical tube-like calyx which is fixed by an irregular expanded 
base. On the upper edge of the cup are five unequal articular 
surfaces for the attachment of the second radials [%.e., IBr]. 
Arms ten, massive, and closely inrolled. Disk relatively small, 
with a central mouth protected by five oral plates, between 
which and the edge of the cup is a very narrow irregular pave- 
7 Crinoiderne i Danmarks Kridtaflejringer, 1913; Jaekel in Pal. 
Zeitschr., 1914, p. 390. 
8 Challenger Reports, part 32, Stalked Crinoids, pp. 197-217. 
