BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. IO.S 



gravelly and stony bottoms is 3.7, that for sandy bottoms being 2.8, and that for muddy 

 bottoms being 2.0. 



The same fact is shown by an enumeration of those species which were taken at 

 one-half or more of the dredging stations on each type of bottom. Four species (Crisia 

 eburnea, Bugula turrita, Schizoporella unicornis, and Smittia trispinosa nitida) are recorded 

 as present in more than half of the dredge hauls made upon gravelly or stony bottoms ; a 

 single species (Bugula turrita) is listed for as great a proportion of the dredge hauls upon 

 sandy bottoms; while not a single species was found with sufficient frequency upon 

 muddy bottoms to appear in this list." 



It is obvious, however, that no such bare characterization of the type of bottom 

 properly describes the habitat of a fixed organism which depends for support upon the 

 presence of some solid substratum. Now various solid objects, organic and inorganic, 

 are commonly present, even upon bottoms of practically pure sand, and such objects 

 frequently furnish attachment for Bryozoa. Even soft mud commonly contains dead 

 shells or fragments of these, and some typical fixed organisms, such as the coral Astrangia 

 and the serpulid worm, Hydroides, are consequently of frequent occurrence upon muddy 

 bottoms. We believe, nevertheless, that the comparative paucity of Bryozoa upon 

 such bottoms is due in part to the scarcity of suitable objects for attachment. Thus 

 the relative infrequency of Cellepora americana and Hippothoa hyalina in Buzzards 

 Bay is probably correlated with the scarcity of hydroids and algae. On the other hand, 

 it seems probable that the continued deposition of silt is unfavorable to the growth of 

 manv forms, even though a suitable basis of support be present. 



Grouping those species which have been charted by us, according to whether their 

 distribution is general or restricted, we may arrange them provisionally under two 

 heads. In making this classification, the greater absolute number of dredging stations 

 in Vineyard Sound must be taken into account. 



Species having a general or unrestricted distribution in local waters. 



Schizoporella biaperta. 

 Lepralia americana+pallasiana. 

 Lepralia pertusa. 



Smittia trispinosa nitida. 

 Hippuraria armata. 



Crisia eburnea. 

 iEtea anguina. 

 Bugula turrita. 

 ?Membranipora pilosa. 

 Membranipora aurita. 

 Schizoporella unicornis. 



Thus the majority of our commoner species do not appear to show any marked pref- 

 erence for one or the other body of water. One of the foregoing species (Membranipora 

 pilosa) appears, however, to display an avoidance of the more central regions of the 

 Bay. In the above fist it will be seen that both erect and incrusting forms are included. 



Species restricted wholly or mainly to Vineyard Sound. 



Number of stations. 



Bicellaria ciliata 16 Sound+ 3 Bay. 



Membranipora tenuis 59 Sound-}- 17 Bay. 



Membranipora flemingii 12 Sound + o Bay. 



Cribrilina punctata 12 Sound+ o Bay. 



Hippothoa hyalina 26 Sound-f- 7 Bay. 



Cellepora americana 66 Sound-)- 13 Bay. 



« It must be added, however, that the lists (pp. 70, 71 above) of species present in one-fourth or more of the dredge hauls 

 upon these respective types of bottom comprise about equal numbers of Bryozoa. 



