BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 63 



of the species in question have been portrayed more fairly, on the whole, than if the 

 supplementary records had been omitted. 



Without making certain allowances one might be greatly misled by these charts. 

 Some of the sources of possible misconception have just been referred to. For all groups 

 the greater apparent abundance of various species in Vineyard Sound, as compared with 

 Buzzards Bay, is frequently to be explained merely by the greater number of dredging 

 stations in the former. The Fish Hawk was employed during two seasons upon the 

 Vineyard Sound series of stations, while systematic dredging by this vessel in Buzzards 

 Bay was limited to the summer of 1904. Thus there are 218 Fish Hawk stations in Vine- 

 yard Sound and only 66 in Buzzards Bay, although the latter is a considerably larger 

 body of water. The concentration of stations in the Sound, so obvious upon the chart, 

 is thus explained. The latter condition is emphasized by the inclusion in the distri- 

 bution charts of records from the "bis" stations (see above), all of which were in Vine- 

 yard Sound. This disparity in the thoroughness with which the two bodies of water 

 were worked was due (1) to the fact that the earlier and more or less experimental 

 dredgings were conducted in Vineyard Sound, and it was regarded as desirable to repeat 

 these; and (2) to the greater uniformity of conditions throughout the bottom of Buz- 

 zards Bay, rendering it unnecessary to dredge at such frequent intervals. 



Another point for which allowance must be made is the fact that the apparent 

 absence of a species from a given area is in some cases due merely to the absence, for the 

 time, of a collector accustomed to search for this particular form, or even to the lack 

 of dredging apparatus suitable for bringing it up. Such cases, and other possible 

 sources of error, will be discussed in their proper places in connection with particular 

 groups of animals. 



Finally, reference must be made to certain spurious distribution patterns, which 

 result, not from any defect in our own methods, but from the transportation of organic 

 remains to points where the animals themselves had probably never lived. As an 

 illustration of this phenomenon we may mention the occurrence of shells of the common 

 oyster in the deeper parts of Vineyard Sound, where their presence is probably to be 

 attributed to passing vessels. Another instance is the transportation of littoral shells 

 (e. g., Littorina litorea) by hermit crabs, and it is likely that the lighter shells of certain 

 mollusks and the remains of various other organisms are carried to considerable distances 

 by currents. 



The distribution charts are reproduced from maps plotted out by Mr. James W. 

 Underwood and Miss Edith Chapman. These assistants employed a blank form based 

 upon a chart prepared by the draftsman of the Bureau, Mr. W. F. Hill. The stars were 

 first put in with a rubber stamp and then filled out with a drawing pen and india ink. 

 Owing to the crowding of stations or the proximity of some of these to shore, the star is, 

 in many cases, at some distance from the station to which it belongs. 



It has not been thought worth while to plot the distributions of any species which 

 were taken at less than 10 of the stations. On the other hand, the distributions of all 

 animals," with a few special exceptions, which were listed from 10 or more stations 

 have been presented herewith. Thus the charts are restricted to the more representa- 



o This statement does not strictly hold for the plants. 



