BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. MSs 
to the inshore stations. The case of Crepidula convexa is peculiar, inasmuch as the two 
other local species of Crepidula are both of very general distribution. The distribution 
of this species is particularly unintelligible, in view of the fact that none of our hermit 
crabs, upon whose shells it finds lodgment, are in any degree restricted to the shallower 
waters along shore. Yet this mollusk was recorded from 45 of the Phalarope and Blue 
Wing stations, as compared with only 16 Fish Hawk stations; and of these last, indeed, 
there is reason for regarding a considerable number as doubtful. This species is known 
to be the commonest Crepidula upon the smaller hermit crabs in shallower waters 
near shore, but it is difficult to understand why this mollusk is not more frequently 
carried by its hosts into the deeper waters as well. 
As in the case of the Pelecypoda, certain species of gastropods are restricted to the 
colder waters of the Sound. The only two to be mentioned are Buccinum undatum and 
Crucibulum striatum. The former was likewise taken at 6 of the 7 regular stations at 
Crab Ledge, and is known to be a predominantly northern species. Such is not true 
of Crucibulum, however, and we are at a loss to explain this peculiarity in its local 
distribution. 
Both of these species (and these alone among the gastropods) were taken pre- 
dominantly at depths of 10 fathoms or more. In fact Crucibulum was dredged only once 
by the Phalarope, and was never taken in less than 10 fathoms of water. 
Certain species among those charted are seen to be less common, or to be wanting 
altogether, in the western half of the Sound, although present in the eastern half. Such 
are Cerithiopsis emersonti and Vermicularia spirata. ‘Two others (Eulima conoidea and 
Seila terebralis) might also be mentioned here, though neither has been taken with 
sufficient frequency to warrant our drawing any general conclusions. 
The distributions of two species of gastropods as portrayed upon our charts are 
obviously largely fictitious. We refer to Littorina litorea and Ilyanassa obsoleta, both of 
which are known to be restricted, when living, to the immediate vicinity of the shore. 
The broadcast way in which the shells of these species, particularly the former, are 
strewn around the local sea floor testifies strongly to the part played by hermit crabs in 
transporting them. 
Several genera comprise species which display among themselves interesting differ- 
ences of habitat. Such are Busycon, Crepidula, Littorina, and Polynices. For most of 
these the differences may readily be seen by reference to the charts. The case of Crepi- 
dula has just been discussed; that of Polynices receives some mention in chapter v 
(p. 186). As regards Littorina, only one species is represented upon our chart, and this 
latter in no way represents the distribution of the living animals. In the catalogue of 
species (section tt), however, the differences in their respective habitats have been 
briefly indicated. 
A glance at the subjoined lists shows that our local assemblage of gastropods, or at 
least the commonest and most representative among them, are even more dominantly 
southern than are the pelecypods. Of the 27 species there considered, 22 are to be 
regarded as southern, 3 as northern, while the remaining 2 are not to be assigned to 
either category. 
Predominantly northern (3). 
Buccinum undatum (chart 166). ...Arctic Sea to Charleston Harbor. 
Polynices heros (chart 187)....... Labrador to Virginia. 
Polynices triseriata (chart 188)..... Labrador to off Hatteras. 
