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 Phalaropc 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 burro\\dng 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 pelecypwds. 



Of general distribution. 

 Busycon canaliculatum. 



Tritia trivittata (commonest recorded species). 

 Anachis avara. 



Urosalpinx cinereus (comparatively few in middle of Bay). 

 Turbonilla sp. sp. 

 Crepidula fomicata. 

 Crepidula plana. 

 Polynices duplicata. 

 Polynices triseriata. 



General in Sound: in Bay mainh' 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 undatura. 

 Crucibulum striatum. 



Polynices heros. 



Restricted mainly or wholly to Buzzards Bay. 

 Tomatina canaliculata. 

 Cylichnella oryza. 

 Busycon carica. 



Ilyanassa obsolcta (mostly in upper half of Bay). 

 Eupleura caudata (in Sound, mainly near shore). 

 Bittium altematum (adlittoral). 

 Caecum cooperi (adlittoral). 



The last two species (Bittium altematum and CcEcum cooperi) were confined almost 

 wholly to the inshore stations of the Bay. Two other species, Lacutia puteola and 

 Crepidula convexa, while found alike in the Sound and the Bay, are restricted in both largely 



