80 



GUIDE TO LOCALITIES. 



species feeds on hydroids, and its narrow foot adapts it eminently 

 for creeping over these small creatures. It will be found commonly 

 in the collecting bottles, after they have stood for a time ; but is 

 not noticsd generally amongst the hydroids on the piles. 



On the fronds and among the roots of Laminaria, whick ar« 

 frequently caught on the piles, many interesting species may be 



«=^5;^. 





Metridium marginatum fully expanded and partly contracted. 

 (After Fewkes; through the courtesy of the Essex Institute.) 



obtained. Obelia geniculata often covers the fronds thickly, giving 

 their surfaces a downy appearance when floating im the water. 

 This species is a native of the cold water of the outer shore 

 and is seldom obtained alive except in its natural habitat. The 

 drainage-polluted water of the Beverly estuary is especially unfa- 



