BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 



69 



Ampiiinsura: 



Chaetopleura apiculata (23). 

 Gastropoda: 



Busycon canaliculatum (24). 



Tritia trivittata (85). 



Anachis avara (64). 



Astyris lunata (54). 



Eupleura caudata (37). 



Urosalpinx cinereus (39). 



Gastropoda —Continued. 



Bittium alteraatum (37). 



Littorina litorea (54). 



Crepidula fornicata (72). 



Crepidula convexa (32). 



Crepidula plana (58). 



Polynices duplicata (36). 



Polynices triseriata (30). 

 Tunicata: 



Didemnum lutarium (27). 



The total number of species in the foregoing list (54) is exactly the same as that 

 contained in the one immediately preceding it. In fact there has been a rather striking 

 uniformity in the numbers comprised in these lists, ranging as they do from 46 to 55. 

 Of the 54 species in the foregoing table, 41 (76 per cent) are common to this and to the 

 list of Fish Hawk species in Buzzards Bay. On the other hand, a number not much 

 inferior to this (37 = 69 per cent a ) are common to the present list and to that given 

 for the Phalarope stations of Vineyard Sound, among the latter being some which are 

 not recorded in the other Buzzards Bay list. A few others in this list are only found 

 elsewhere in the Fish Hawk list for Vineyard Sound. 



While, therefore, the Phalarope list for Buzzards Bay resembles the Fish Hawk list 

 for Buzzards Bay more closely than any of the others, it must be pointed out that it 

 contains a considerable number of species which are prevalent throughout the Sound, 

 but which in the Bay are to be found only at the inshore dredging stations. This fact, 

 which is not very strikingly illustrated by these figures, will appear much more clearly 

 when the charts portraying the distribution patterns of certain species are scrutinized. 



Tables have likewise been prepared listing the "prevalent" species for each type of 

 bottom. The same criterion has here been employed of admitting only those species 

 which have been encountered at one-fourth or more of the number of stations belonging 

 to the group in question. 



After considerable thought the following classification of bottoms has been adopted 

 for present purposes, not as being an ideal one, but as being the most simple one possible 

 consistent with a fair regard for accuracy. The only strictly exact classification would 

 recognize as many types of bottom as there are combinations of ingredients listed; but 

 such a classification would be altogether too cumbersome for the purposes of our statis- 

 tical treatment. We realize that the grouping here employed must result in a quite 

 inadequate characterization of the habitat of many species. A specimen may ostensibly 

 have come from a muddy or a sandy bottom, when, in reality, it was growing attached 

 to a shell or other solid object. We have, nevertheless, included as muddy and sandy 

 those bottoms in which shells were likewise recorded. This has been done for the reason 

 that shells or fragments of these were scarcely ever wholly lacking from the contents 

 of the dredge. Again, certain living mollusks which move freely over the bottom afford 

 support for attached organisms just as well as do dead shells. Surely the presence of 

 such should not suffice to constitute a "shelly" bottom. The same may be said regard- 

 ing shells occupied by hermit crabs, which abound throughout the entire region, giving 

 support to hydroids, Bryozoa, barnacles, Crepidulae of several species, and other 

 organisms. 



Only ss per cent of the Fish Hawk list for Buzzards Bay were common to the Fish Hawk list for Vineyard Sound. 



