STUDIES IN MARINE ECOLOGY. 173 



results obtained by the dredgings of the Biological Survey with 

 our main work further inshore. 



A Habitat Check List of the Common Invertebrate 



Animals of the Woods Hole Littoral with 



Distribution Records for 1920 and 192 1. 



The appended list of animals is based on all the collecting 

 done since 1912. The distribution records are based on the 

 reports from operations in 1920 and 1921. The statistics given 

 are from team records. Thus in these two years, two teams 

 collected Chalina from the mud, eight teams have recorded it 

 from rocks, ten from wharf pilings and nine from dredging. 

 The figures given show no indication of the number of specimens 

 taken other than that suggested by the fact that the more 

 animals present, the greater the probability that all teams would 

 find them. Anyone interested in the abundance of these animals 

 in particular localities is referred to the second study in the 

 present series. 



The tabulation is from the reports of 30 collecting teams 

 operating on wharf pilings; 52 from sand, mud, gravel and eel 

 grass; 56 teams from rocks and 42 from dredging. The records 

 of plankton have been kept in a different way and the presence of 

 recognized animals in late July or early August is merely checked. 



The classification of habitats in the field has sometimes been 

 left to the judgment of the student recorder and it is entirely 

 probable that some of the 52 recorders thought a given habitat 

 was best recorded as "sand" while others regarded animals from 

 a similar place as "mud" dwelling. All gradations between the 

 two exist and the conditions under which the collecting was done 

 do not permit a more refined grading. The error arising from 

 this source is somewhat compensated by the fact that no dragnet 

 collections were made as it was desired to find where individual 

 animals live as well as to collect different species. 



Unidentified animals have not been included in the habitat 

 list unless the genus, at least, could be determined with some 

 assurance. All the records are for living animals since for eco- 

 logical purposes the recording of dead shells can only be worth- 

 less and confusing in a region where tidal currents run strongly 

 and where the shore birds distribute shells even over the land. 



