456 BULLETIN OF THE BUREAU OF FISHERIES. 



and East Chop. The lower portion of the Bay and the westerly portion of the Sound 

 have in the summer a flora, here termed the cool-water sublittoral formation, with a 

 number of striking peculiarities, while the more sheltered regions have in the summer 

 a strictly warm- water sublittoral formation. 



Only the most striking of the algal associations and formations will be described, 

 for this is a subject which might be followed into such detail that the broad and striking 

 peculiarities would be lost among the minor features. Moreover, for the reasons given 

 above, the physiographical features and other conditions of Woods Hole do not lend 

 themselves to the development of picturesque algal associations. 



ALGAL ASSOCIATIONS. 



(i) THE LYNGBYA SALT-MARSH ASSOCIATION. 



The bottom and sides of shallow bodies of water in salt marshes, and other brackish 

 ditches and pools, are frequently covered by felted growths, which are largely composed 

 of Lyngbya, most commonly the species L. cestuarii and L. semiplena. Mixed with the 

 Lyngbyas may be found Chroococcus turgidus, Microcoleus chthonoplastes, Microcoleus 

 tenerrimus, Spirulina subsalsa, Anabcsna torulosa, Nodularia Harveyana, and other forms. 



This is a very characteristic association of blue-green algae frequently forming 

 extensive growths in the summer months in the salt marshes and brackish pools of 

 Quisset, Penzance, and Hadley Harbor. 



(2) THE ENTEROMORPHA SALT-MARSH ASSOCIATION. 



Brackish pools in salt marshes and other situations frequently contain extensive 

 floating or loosely attached growths, which are chiefly species of Enteromorpha, the 

 commonest species being E. clathrata, E. crinita, E. percufsa, and E. prolifera. Clado- 

 phora expansa is found under similar conditions, frequently mixed with the Entero- 

 morphas. 



This association of green algae forms surface growths in situations where the Lyngbya 

 association is likely to be found over the bottom. It is frequently conspicuous during 

 the summer months in brackish pools of Quisset, Penzance, and Hadley Harbor. 



(3) THE CALOTHRIX ASSOCIATION. 



Of the four species of Calothrix which may be found on stones and woodwork 

 between tide marks, C. pulvinata is the most conspicuous, developing thick patches 

 resembling honeycomb on the woodwork of wharves (wharf of U. S. Bureau of Fisheries). 

 Calothrix scopulorum, also conspicuous, grows on rocks near high-water mark or above, 

 occasionally in company with Codiolum gregarium, forming large indefinite patches; it 

 also grows on piles. 



(4) THE RIVULARIA ASSOCIATIONS. 



Rivularia nitida is found in salt marshes (as at Quisset) forming thick growths over 

 mud and roots of Spartina well above low-water mark. Rivularia atra is occasionally 

 plentiful on rocks and barnacles near high-water mark. 



a Geographically this region might be considered as a portion of Nantucket Sound if one were disposed 10 draw an 

 arbitrary line between Vineyard Sound and that body of water. 



