934 CHARLES ZELENY 
branchia of the opposite side drops off, the break appearing at 
the base of its stalk. In its place a bud-like rudimentary oper- 
culum is developed (fig. 5). There is then on the left side a func- 
tional operculum with a naked stalk and a terminal cup’ bearing 
—SJ 
q = 4 y 
Fig. 4 Hydroides dianthus, age 26 to 28 days but further advanced than the in- 
dividual shown in fig. 3. Stage with four pairs of branchiae. Figure shows the 
three most dorsal pairs. The ventral pair is directed away from the observer 
and is not shown. The opercular knob of the left side is notched and its stalk 
still retains the respiratory pinnules. The branchia next to the dorsal one of the 
right side has eight pinnules but differs from the other branchiae, except the oper- 
cular one, in the absence of new pinnule buds. A, level of cut in individual A, 
(no. 2778); B, level of cut in individual B, (no. 2779); Ba, regenerating functional 
operculum one day after operation in individual B. 
a single row of serrations, and on the right side a rudimentary 
operculum. The characteristics are those found in the adults 
of the genus Serpula except for the fact that in Serpula the func- 
tional operculum may be either right or left (fig. 6, £). 
