126 MARINE INVERTEBRATES 
six tentacles and numerous eye-spots. When disturbed it flattens its 
disk and folds together, leaving its tentacles sprawled in every direction. 
It is very languid in its movements, and often remains in one position 
for hours. These meduse are found only in the hottest hours of the 
day, but are very plentiful then, shoals of them often stretching for 
miles, and so thick as to touch one another. Their habitat is the New 
England coast. 
Genus Clytia 
C. poterium. This hydroid is found creeping over seaweeds in tide- 
pools from Long Island Sound northward. The main stem is prostrate, 
or root-like, running over the body to which it is attached. The stems 
rise as do the tubularians. The sterile zodids are on single stems about 
one quarter of an inch high. The stems are faintly ringed for their 
entire length, and at the top have a distinct ring, on which rests an open, 
bell-shaped cup, which is smooth around the rim. The reproductive 
zo0ids are on very short pedicels, and the cups are long and cylindrical, 
with a wavy outline. (Plate XLII, A.) 
C. bicophora. This species is found in the same places as the pre- 
ceding, and is of about the same size. The long stems are more or less 
ringed and sometimes branched. The edges of the cups are notched. 
The medusa-buds are urn-shaped and ringed, and are on very short 
pedicels. (Plate XLII.) 
THE SERTULARIANS 
The sertularians are distinguished by the horny cup, which is 
sessile—that is, set directly against the stem instead of being 
raised upon a stalk. They are among the most common objects 
of the beach, and, like the plumularians, are often mistaken for 
plants by the amateur collector and are gathered and pressed as 
seaweeds. They are found everywhere along the coast. They 
zigzag over the fronds of seaweeds or hang in fringes upon them, 
as well as upon rocks, stones, and shells. They well repay close 
examination with a glass. Every open cup bears a wreath of 
tentacles, which makes the branch a spray of stars. This is not 
an inappropriate comparison, for besides their starry shape some 
species emit a phosphorescent light. 
Genus Sertularia 
S. pumila. The most abundant of all the hydroids on the northeast 
coast is this species, which is found in profusion upon Fucus and other 
seaweeds, and mingled with them upon the rocks. It is easily distin- 
guished from the campanularians because its zodid-cups are close against 
the stems (sessile) instead of on stalks or pedicels. The stem creeps 
