64 BULLETIN OF THE BUREAU OF FISHERIES. 



tive species comprised in our local benthos. In many cases, however, highly instructive 

 data have been obtained regarding forms of less frequent occurrence. Such have been 

 referred to in the text. 



Records entered as doubtful have been excluded in plotting the distribution charts. 

 In the charts for the shell-bearing mollusks and echinoderms, and for the coral Astrangia, 

 it will be found that the stars are in many cases surrounded by circles. The circle in 

 each case indicates that one or more living specimens were recorded from the station in 

 question; absence of the circle implies either that the records indicate the presence of 

 dead shells only, or that no statement has been made on the subject. 



3. THE FAUNA CONSIDERED ACCORDING TO REGIONS AND HABITATS. 



Many of the species encountered during our dredging operations were found to 

 have a practically unrestricted distribution within the waters explored. In the case 

 of many other species, their distribution was found to be definitely restricted, i. e., 

 they were adapted to particular temperatures or to particular kinds of bottom. These 

 various types of distribution will be discussed at some length in relation to particular 

 species which serve to illustrate them, and many cases are portrayed graphically by 

 means of charts. But it is likewise important that a list of the more prevalent species 

 should be presented synoptically for each subregion of our chart and for each variety of 

 habitat. With this in view the stations were tabulated in various ways, according to 

 the type of bottom or the like; and for each of these groups lists were prepared 

 comprising all of those species which were taken at one-fourth or more of the stations 

 in question." We believe that lists thus restricted may be regarded as comprising 

 only such species as are truly representative of these various bottoms. It must be 

 conceded, however, that many of the less common forms which do not appear in the 

 lists at all may be highly characteristic of one or another group of stations, and may, 

 indeed, be limited to these. 



Preceding the lists for particular waters or particular types of bottom we present a 

 table comprising those species which were taken at one-fourth or more of the total 

 number of dredging stations of the Survey, i. e., at 115 or more of the regular stations. 6 

 It is believed that such a list conveys a good idea of the prevailing benthic fauna of our 

 local waters, so far as we can speak of any single prevailing fauna where the conditions 

 differ so widely. This list will perhaps render possible the detection of future changes in 

 the relative abundance of certain species. 



a At first only those species were listed which were present at half or more of a given group of stations, but it was found that 

 all of the resulting lists were very brief, and that they omitted many highly characteristic forms. 



b None of the supplementary stations, except the "bis" stations of 1904, have been considered in the present computations. 

 The inclusion of the 1909 records would doubtless change the complexion of these tables somewhat, though not, we believe, very 

 materially. 



