152 BULLETIN OF THE BUREAU OF FISHERIES. 
As in the case of the lamellibranchs, the average number of gastropod species taken 
per dredge haul was considerably greater for Buzzards Bay than for Vineyard Sound. 
This statement applies equally to the Fish Hawk and the Phalarope stations. The 
average number for dredge hauls upon muddy bottoms (7.8) is likewise seen to exceed 
that for the other types of bottom, though the difference is much less pronounced than 
for the bivalve mollusks; while the figure for sandy bottoms (6.5) is seen to be practically 
the same as that for bottoms of gravel and stones (6.7). The difference, in this respect, 
between the two chief classes of mollusks is doubtless due to the fact that the Pelecypoda 
comprise a considerable proportion of burrowing forms. 
Reference to the tables giving the “prevalent”? species for each type of bottom 
shows that there are 8 such species recorded for sandy bottoms, 9 for gravelly and stony 
ones, and 11 for muddy ones. Of these, 7 species (or their shells, at least) are common 
to the three lists. 
Charts 162 to 188 portray the distribution of most of those species which were 
recorded from 10 or more of our stations in Vineyard Sound and Buzzards Bay. The 
exceptions are Natica pusilla, for which no chart has been presented, owing to the 
ambiguity of many of the records (see p. 144), and certain species of Turbonilla, several 
of which were doubtless taken with considerable frequency. Owing to a confusion, 
already referred to, in our original records we have devoted a single chart to all the 
members of this genus, so far as recorded by us. 
In respect to their distribution in local waters, we may group the gastropods in 
much the same way as has already been done for the pelecypods. 
Of general distribution. 
Busycon canaliculatum. 
Tritia trivittata (commonest recorded species). 
Anachis avara. 
Urosalpinx cinereus (comparatively few in middle of Bay). 
Turbonilla sp. sp. 
Crepidula fornicata. 
Crepidula plana. 
‘Polynices duplicata. 
Polynices triseriata. 
General in Sound; in Bay mainly confined to inshore stations. 
Astyris lunata. 
Cerithiopsis emersonii (hardly general in Sound). 
Vermicularia spirata (hardly general in Sound; mostly confined to eastern half). 
Restricted mainly or wholly to Sound. 
Buccinum undatum. 
Crucibulum striatum. 
Polynices heros. 
Restricted mainly or wholly to Buzzards Bay. 
Tornatina canaliculata. 
Cylichnella oryza. 
Busycon carica. 
Ilyanassa obsoleta (mostly in upper half of Bay). 
Eupleura caudata (in Sound, mainly near shore). 
Bittium alternatum (adlittoral). 
Czcum cooperi (adlittoral). 
The last two species (Bittium alternatum and Cecum cooperi) were confined almost 
wholly to the inshore stations of the Bay. Two other species, Lacuna puteola and 
Crepidula convexa, while found alike in the Sound and the Bay, are restricted in both largely 
