BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 181 
5. POSITION OF THE LOCAL FAUNA IN ZOOGEOGRAPHY. 
Certain questions will naturally present themselves to the student of geographical 
distribution: What is the position of the Woods Hole fauna in the fauna of our American 
coast? To which of the larger zoogeographical regions does it belong? And is it 
situated in the middle of that region or close to one of its limits? In other words, do 
the majority of species have a range which extends mainly to the northward along this 
coast, or do the majority have, on the whole, a southward range; or is there no appreci- 
ble preponderance of one sort over the other? Simple as these questions may seem, 
it is difficult to give them an answer that is at all satisfactory. The known range, as 
distinguished from the actual range, of a species, is very frequently determined by 
historical accident. Thus the Bay of Fundy, Massachusetts Bay, Woods Hole, Newport, 
New Haven, Charleston, etc., frequently figure in our literature as limits of distribution, 
and this for reasons which are obvious to anyone familiar with the history of American 
marine zoology. Verrill and Smith, in their Vineyard Sound report, give Cape Cod as 
the southern limit, or the northern limit, of distribution for many species whose known 
range has since been extended far beyond this point. 
Likewise the impossibility must be borne in mind of forming a just estimate of the 
geographical range of a species from any mere statement, however correct in itself, of 
the extreme limits of its distribution. The bathymetric range and other factors of its 
habitat at various latidudes must be taken into consideration. It was long ago pointed 
out by Edward Forbes (1844, p. 323) that ‘“‘parailels in depth are equivalent to paral- 
lels in latitude.”” Walther (1894) states that from the surface down the temperature 
declines about 1° C. for each 18 meters. Accordingly, a species which is truly ‘‘boreal”’ 
in its general tendencies, and which occurs in abundance along the littoral zone, in 
northern latitudes, may none the less be found in the deeper colder waters of a region 
far to the southward. To state such a range merely in terms of latitude would be 
highly misleading. Again, it is obvious that the same importance must not be attributed 
ta the isolated and occasional occurrence of a given species as to its occurrence at points 
where it is widespread and abundant. But in many of the tables which are available 
for consultation no distinction is made between the two. 
Furthermore, the question as to the position of the Woods Hole fauna, from the 
standpoint of zoogeography, can not be answered until we have made clear what is to 
be understood by the “Woods Hole fauna.’ If by this expression'we are to mean the 
aggregate number of species which have ever been taken within the limits adopted, the 
question would be a difficult one to answer, and the answer, when given, would be of 
little value. Such an inclusive list (which would be coextensive with our own annotated 
list or catalogue) would comprise not only the truly indigenous species, characteristic 
of the region, but the occasional stragglers borne from southern waters by the Gulf 
Stream, and likewise those northern forms which we have met with only at Crab Ledge 
or in the colder waters off Gay Head. These are mostly rare species locally, and are 
in no sense characteristic of the shallower waters of this section of the New England 
coast, yet the total number of such species is very considerable. In practice, however, 
it is difficult to separate the truly indigenous types from those which are to be regarded 
as exotics or stragglers. An arbitrary basis of selection must therefore be adopted. 
For the purposes of the ensuing analysis we have included as representative local species 
only those which have been taken at 10 or more of the dredging stations. There are 
