BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 139 
Of the 13 species for which distribution charts have been presented, 8 are of more 
or less general occurrence throughout the Sound and the Bay, so that their distribution 
bears little apparent relation to the character of the bottom. For this reason no such 
sharp division between Bay-dwelling and Sound-dwelling species can be made here, as 
was possible, for example, with the Annulata. The species whose distribution is most 
clearly determined by the nature of the bottom is the “lady crab,”’ Ovalzpes ocellatus. 
It will be seen from the chart that this crab is for the most part restricted to the 
western half of Vineyard Sound, where the bottom is known to consist for the most 
part of clear sand. That this peculiarity in the distribution of Ovalzpes is related to 
the character of the bottom is shown by the fact that it was dredged by us several 
times near the head of Buzzards Bay, i. e., in the warmest waters of the region, while 
it is a matter of common knowledge that this species frequents sandy bottoms in 
shallow water. 
Other species which appear upon the chart as restricted wholly or chiefly to 
Vineyard Sound are Pinnotheres maculatus, Cancer borealis, Pelia mutica, and Pagurus 
acadianus. ‘The first of these is commensal in the mussels, Modiolus modiolus and 
Mytilus edulis and in the common scallop, Pecten gibbus. The distribution is thus 
dependent upon that of the hosts. The most frequent host, Modiolus modtolus, was, 
however, very scarce in Buzzards Bay, while Mytilus was found living only near the 
lower end. The occurrence of this species in the dredging records is likewise dependent, 
of course, upon whether or not the mussels from a given station were opened and 
examined for the crabs. This was probably done more commonly in Vineyard Sound 
than in Buzzards Bay. Pinnotheres has been taken by us at two supplementary stations 
in the Bay, on one occasion in Pecten, on the other in Modtolus. 
Cancer borealis was recorded from only one regular station in the Bay,? and its 
occurrence there is certainly infrequent. It is most common at the western end of 
Vineyard Sound, though taken sparingly throughout its length. The absence of this 
species from the Bay is probably due in part, at least, to the temperature factor. 
Pelia mutica is much less common in the Bay than in the Sound, and its occurrence 
in the former is restricted mainly to the inshore stations. The distribution of this 
species displays certain other peculiarities which will be discussed under the head of 
temperature. 
Pagurus acadianus was not recorded once from the Bay, nor indeed was it recorded 
from the eastern half of Vineyard Sound. Here, too, temperature rather than bottom 
seems to be the determining factor. 
As is well known, the distribution of many of the littoral species of decapods is 
conditioned by the character of the shore. Certain forms (e. g., the fiddler crabs) are 
chiefly confined to muddy situations; others (Palemonetes vulgaris and Hippolyte 
zostericola) are found mainly in the beds of eel grass, while the common “‘Hippa’”’ burrows 
in the sand at low-tide mark, etc. It is therefore rather surprising to find how few of 
the deeper water species are distributed in accordance with the character of the bottom. 
Much more striking, on the other hand, are the examples of distribution in accord- 
ance with temperature. While many of our species display no restriction whatever in 
relation to this factor, certain others are pretty definitely limited to the colder waters 
of the region, while others still appear to avoid these colder waters, although elsewhere 
4 J,ater at two supplementary stations near the lower end. 
