ECHINODERMATA OF THE BRASSFIELD FORMATION 
7 
outline they are long and linear, with their longer axes directed 
at right angles to the length of the brachiole. The ambulacral 
plates which remain attached to the theca of the species of 
Brockocystis here under discussion appear to be of comparatively 
large size and are relatively few in number. 
The semilunate pore (gonopore) on plate 23 is distinct y de- 
fined in the angle between the two ambulacra which extend to- 
ward plates 17 and 18. A more minute pore (hydropore) may 
be present directly beneath the center of the semilunate pore, 
but is not distinctly defined. Plate 23 may be a double plate; 
at least, a crack appears to pass through the center of the semi- 
lunate pore. 
The largest fragment of a column remaining attached to any 
theca known is 20 mm. in length. In the more distal parts of 
the column, for a length of 12 mm., the column is narrow, ranging 
from two-thirds to a whole millimeter in width, the proximal 
columnals being broader. In the prox'mal part of the column, 
8 mm. in length, the columnals are collected into two groups, 
of which the first is inversely pyriform, and the second is inversely 
truncate-conical in form. The constituent columnals of each 
group are anchylosed together, but the groups separate readily 
from each other and from the remainder of the column. In this 
separated condition the groups form characteristic fossil remains 
easily identifiable generically, even in the absence of the theca. 
This is true especially of the inversely pyriform groups. A 
vertical section of one of these groups (fig. 5) shows a lumen 
from three-fourths of a millimeter to a whole millimeter in width. 
Along this lumen, the constrictions locating the inner parts of 
the columnals appear equally spaced, six columnals occupying 
a length of slightly more than 3 mm. Exteriorly, the marginal 
parts of the constituent columnals of the inversely pyriform 
groups rise, so that externally the lower three or four columnals 
of each group appear distinctly longer than the upper three or 
four columnals of the same group. The topmost columnal is 
constricted in size to the width of the lowest columnal, and is 
hidden in the base of the large depression indenting the top 
of the group. To this hidden columnal is attached the second 
