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. 
(1) 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. estuarw and L. semiplena. Mixed with the 
Lyngbyas may be found Chroococcus turgidus, Microcoleus chthonoplastes, Microcoleus 
tenerrimus, Spirulina subsalsa, Anabena torulosa, Nodularia Harveyana, and other forms. 
This is a very characteristic association of blue-green alge 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 EF. clathrata, E. crimta, E. percursa, and E. prolifera. Clado- 
phora expansa is found under similar conditions, frequently mixed with the Entero- 
morphas. 
This association of green alge 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 mtida 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. 
@ Geographically this region might be considered as a portion of Nantucket Sound if one were disposed to draw an 
arbitrary line between Vineyard Sound and that body of water. 
