BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 1 39 



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," Ovalipes 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 Ovalipes 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 modiolus, 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 Modiolus. 



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) arc 

 chiefly confined to muddy situations; others (Palcemonetes vulgaris and Hippolytc 

 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 



« Later at two supplementary stations near the lower end. 



