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 medusae 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 zooids 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 

 zooids 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 zooid-cups are close against 

 the stems (sessile) instead of on stalks or pedicels. The stem creeps 



