BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 105 
‘ 
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 turrata, Schizoporella unicorns, 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 A strangia 
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 alga. On the other hand, 
it seems probable that the continued deposition of silt is unfavorable to the growth of 
many 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. 
Crisia eburnea. Schizoporella biaperta. 
Altea anguina. Lepralia americana-+ pallasiana. 
Bugula turrita. Lepralia pertusa. 
?Membranipora pilosa. | Smittia trispinosa nitida. 
Membranipora aurita. Hippuraria armata. 
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 (Vembranipora 
puosa) appears, however, to display an avoidance of the more central regions of the 
Bay. In the above list it will be seen that both erect and incrusting forms are included. 
Species restricted wholly or mainly to Vineyard Sound. 
Number of stations. 
DESAI Es Mae RAE MER Oh elite Fo Ie ce ah al cli fg 6 cavsigi dfs” sign’ w bse the Foe ld My ek 16 Sound+ 3 Bay. 
Me EERE MIS OCS os oe ae tats Sond Gn 9,4 4 dime oae veh ules 59 Sound+17 Bay. 
Metibrcaitpetty HemIMOIE lee ce ss oe oe oe cee abe s cows een 12 Sound+ o Bay. 
RIEU NE leah Oe Sth ss 5 c+ 6 seed ename 12 Sound+ o Bay. 
HUI ppothGa MM youalee te lone dsettertctete siaet cen sincnndse SO ROLEEHE 7 Bay, 
CONCROED AIeEIACED SS nee Galas co epee tees 66 Sound+13 Bay. 
2 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. 
