BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 



79 



V. Average number of species per dredge haul, showing the representation oj the various 

 groups of animals on each type of bottom. 



Group. 



Porifera 



Hydrozna 



Actinozoa 



Nemertinea. . . 



Bo'ozoa 



Asteroidea. . . . 

 Ophiuroidea. . 

 Ecbinoidea. . . 

 Holothuroidea 

 Annulata ..... 

 Sipunculida. . , 

 Cirri pedia .... 

 Amphipoda.,. 



Isopoda 



Decapoda 



Pycnofionida. , 

 Pelecy poda . . . 

 Amphineura. . 

 Gastropoda . . . 



Tunicata 



Pisces 



Sand. 



o. 5 

 I- S 

 ■3 



•9 

 ■ og 

 I. o 



.02 



3-4 



•°5 



■3 

 1.6 



•S 

 3S 



.OS 

 9.8 



6.5 

 •9 



1.4 



Gravel 



and 

 stones. 



I. o 



1.8 



•7 



■ 01 



3-7 



'•3 



. 01 



4- 7 

 •03 

 ■4 



1.6 



-• 7 

 •3 

 6.7 

 1.9 

 •7 



To what degree such figures as the foregoing, giving the average number of species 

 per dredge haul, represent the actual wealth in species of the various subdivisions of our 

 local sea bottom can not be stated with certainty. Whether, for example, the greater 

 number of species per dredge haul found in Buzzards Bay denotes an actually greater 

 number of species per unit area of sea floor, is not self-evident. It is plain that the 

 dredge must cut more deeply into a bottom of soft mud than into one of hard sand or 

 gravel, and that therefore a larger proportion of burrowing organisms will be obtained 

 in the former. It seems quite possible, therefore, that the excess in favor of Buzzards 

 Bay has been exaggerated, or that it does not exist at all. 



Now, an inspection of table vi, showing the total number of species taken at each 

 of the five groups of stations, reveals the fact that the number of species taken by 

 the Fish Hawk in Vineyard Sound is about 25 per cent greater than that taken in 

 Buzzards Bay. But it must likewise be borne in mind that the number of Fish Hawk 

 stations in Vineyard Sound was over three times as great as that in Buzzards Bay, 

 thus rendering probable the capture of a larger number of the less common species. In 

 fact, it will be noticed that the figures expressing the total number of species for each 

 of these groups of stations may be arranged in the same order as those expressing the 

 number of stations in each group.'' We nevertheless think it likely, in view of all our 

 data, that the actual number of species inhabiting Vineyard Sound is greater than that 

 inhabiting Buzzards Bay. This is probably due to the fact that the bottom of the former 



a That the number of species in each case is in no sense proportional to the nunihcr of stations is. however, riuite plain. 



