BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 77 



Vineyard Sound is not determined by temperature, but by the character of the bottom. 

 Nevertheless, after making these allowances, the significance of the facts discussed upon 

 the last few pages can scarcely be doubted. 



4. THE AVERAGE YIELD OF THE DREDGE HAULS. 



Another method of portraying synoptically the general facies of our local fauna, as 

 revealed by the dredge, is to present the average composition of the dredge hauls. This 

 we have computed for the Survey as a whole, and for the separate groups of stations 

 which have been distinguished above; for the animal kingdom as a whole, and for its 

 main subdivisions. In the following tables certain groups which were represented very 

 sparingly in our dredgings, or which were not looked for systematically, and certain 

 others which do not properly belong to the benthos have been omitted. 



I. Average number of genera and species of animals taken per dredge haul. 



Genera. Species. 



Survey as a whole (458 stations) 34. 3 37° 



Fish Hawk, Vineyard Sound (218 stations) 33. 7 36. 5 



Fish Hawk, Buzzards Bay (66 stations) 36. 3 38. 7 



Fish Hawk, Crab Ledge (7 stations) 37. o 39. 7 



Phalarope and Blue Wing, Vineyard Sound (77 stations) 32. i 35. 2 



Phalarope, Buzzards Bay (90 stations) 36. o 38. 5 



While there is a rather surprising uniformity amongst these figures, it will be noted 

 that the average number of species is slightly greater for the Fish Hawk than for the 

 Phalarope stations; likewise that it is greater for Buzzards Bay than for Vineyard Sound, 

 and greatest of all for Crab Ledge. It is of interest, likewise, that the average number 

 of genera per dredge haul is nearly equal to that of the species. This point will be 

 discussed later. 



II. Average number of gowra and species for the 458 regular stations of the Survey, showing 



representation of each group of animals. 



Group. 



Pori/era 



Hydrozoa .... 



Actinozoa 



Nemertinea . . . 



Bryozoa 



Astcrotdea . . , . 

 Ophiuroidea . 

 Echinoidea . . . 

 Holothuroidea 

 .\nnulata . . . . 

 Sipunculida.. . 



Group. 



Cirripedia. . . 

 Decapod a . . . 

 Amphipoda. 



Isopoda 



Pycnogonida 

 Pelecypoda . . 

 Amphineura 

 Gastropoda . . 

 Cephalopoda 



Tunicata 



Pisces 



Genera. 



Species. 



In the foregoing table, it is nearly certain that the figures for certain groups, 

 especially, perhaps, for the Porifera, do not fairly represent the number of these forms. 

 For this reason, indeed, the Foraminifera have been omitted altogether. As stated in 

 another section (p. 91), the Foraminifera were looked for systematically during one 

 season only, while the Porifera at no time received adequate attention. 



