BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 147 
A study of the distribution charts shows us that, whereas a considerable number of 
our local Jamellibranchs are of very general distribution throughout Vineyard Sound 
and Buzzards Bay, a yet greater number show definite restrictions in relation either to 
the character of the bottom or to temperature. The part played by the bottom in 
determining the wealth of lamellibranch life is indicated to some extent in the figures 
representing the average number of species per dredge haul taken upon the three chief 
types of bottom. These are: Gravel and stones, 7.7; sand, 9.8; mud, 11.0. 
These figures are quite in accord with those giving the average number of species 
per dredge haul in the Sound and the Bay: 
Vineyard Sound: 
BASLE ELAN cer. issu k sc as MC aed cede gah cls RY DEE ROE Lan Oe 8.2 
PPEIAAAES SOY ho cece ACY rises tec kid = Viena oo ee Cece Cee ees 75 
Buzzards Bay: 
LENS! MES Let 2 ag ak RO Ie ae Co een ero eek ee ee TEAS 
ELITE E200 oa A ne aI Baer ee ae a ee eR DE ere oy maca, tS 11.6 
It is not evident, however, why the Phalarope stations of the Bay, which, on the whole 
were decidedly less muddy than the Fish Hawk stations, should none the less show a 
larger number of species. 
The lists of ‘‘prevalent”’ species for the three types of bottom (i. e., those present at 
one-fourth or more of the stations) display a degree of uniformity which was unexpected 
in view of the above shown differences in the wealth of species per dredge haul. The 
number of prevalent species (16) is the same for sandy as for muddy bottoms, while 13 
such species are listed for bottoms of gravel and stones. Of these, 9 are common to the 
three lists. 
Passing to a consideration of the charts (122-160) we find a considerable variety 
among the distribution patterns, but it seems possible to reduce these to comparatively 
few types. These last are not, however, to be distinguished sharply from one another. 
Of general distribution. 
Anomia simplex. 
Pecten gibbus borealis (scarce, however, in center of Bay). 
Arca transversa. 
Nucula proxima. 
Cardium pinnulatum. 
Callocardia morrhuana. 
Tellina tenera. 
Ensis directus. 
Clidiophora gouldiana. 
General in the Sound; common in the Bay, but restricted to inshore stations. 
Crassinella mactracea. 
Divaricella quadrisulcata (only 20 stations altogether). 
Cumingia tellinoides (not exactly general in Sound, and some records for middle of Bay). 
Spisula solidissima (some records for middle of Bay). 
Cochlodesma leanum. 
Corbula contracta. 
General in the Sound; in the Bay, restricted to lower half. 
Mytilus edulis. 
Astarte castanea. 
Petricola pholadiformis. 
