150 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
From the oral disk immediately outside the base of the oral tube 
there arises a row of branching thin-walled organs, which are probably 
to be regarded as gills. Like the marginal tentacles, this row of gills is 
interrupted at the posterior side of the disk, and consequently has the 
form of a horseshoe. There are usually 16 pairs of gills and an odd 
one, making 33 in all; but in one specimen there were only 27 in all, 
and in another there were 37. Mr. Agassiz has sketched one individual 
with only 21. There is considerable variability in the size of the gills; 
the posterior ones, though usually smaller than the anterior ones, are not 
always so. A few small gills are sometimes intercalated between those 
of larger size. Though arranged approximately in a single row, there is 
some irregularity in their position, especially toward the anterior end of 
the disk, where they are more crowded than near the posterior end. In 
fresh specimens they are of a rose-pink color, but in alcohol this color is 
lost. 
Each gill consists of a single cylindrical, or somewhat flattened hol- 
low stalk, terminating in quite regular dichotomously forking branches. 
The stalk rises abruptly from the surface of the disk, sometimes being 
slightly constricted at its base; it has a length of from 4 mm. to 
8 mm., and a fairly uniform diameter of from 0.5 mm. tol mm. The 
forking may extend to the production of branches of the ninth or tenth 
order. The terminal branches, of which there may be nearly 500 toa 
gill, end blindly with rounded tips. In alcoholic material the branches 
are often varicose, owing to distention with coagulated contents. In 
the living condition they are probably of much more nearly uniform 
calibre. When not contracted the gills rise above the oral orifice, and 
even above the oral tentacles themselves. 
Radial canals are traceable running across the disk from the base of 
the oral tube to the bases of the marginal tentacles, before reaching 
which many of them fork, each of the branches communicating with the 
lumen of a single tentacle. 
The outer surface of the calyx constitutes the upper part of the 
column; its height is greatest in front, diminishing to practically zero 
behind. Above the constriction which marks the transition from it to 
the stalk proper, it gradually expands to meet the margin of the oblique 
oral disk. It is marked with fine longitudinal dark lines alternating 
with lighter ones, as in the rest of the column. 
The column resembles that of Cerianthus in being elongated, eylindri- 
cal, and enlarged at its basal end. Below the constriction which marks 
the boundary of cup and stalk it presents a spindle-shaped enlargement. 
