The work was done principally in the months of June, July, 

 August, and September, althoui.h a few samples were taken earlier and 

 a few later in the season. In 1929 and 1930 all of the sampling was 

 done between June l5 and September l5. 



In 1928 quantitative bottom samples were taken with an Ekman 

 dredge 6 inches (l5.2l( centimeters) square. The dredge was identical 

 in construction with the one described and pictured by Birge (1922) . 

 In 1929 this dredge was replaced by one which was 20 centimeters 

 square. The large dredge could be handled almost as easily as the 

 small one, and it took a much larger sample, the small dredge covering 

 232.25 square centimeters and the large one UOO square centimeters. 

 The factors for converting the number of organisms per sample to the 

 number per aquare meter were thus li3 and 25, respectively. 



It is well known that the Ekman dredge works well only on a 

 soft bottom, and for that reason it was replaced in 1930 by a 

 Petersen dredge covering an area 27.3 by 27.0 centimeters or 737 

 square centimeters. The conversion factor was thus 13.5. After apply- 

 ing this factor, fractional niombers were roimded off to the nearest, 

 whole number. The Petersen dredge is so much more efficient than the 

 Ekman dredge on sandy or gravelly bottom that its use is justified on 

 such bottoms in spite of the inconvenience involved. It does not always 

 take a quantitative sample; in fact at certains tations it was found 

 impossible to take more than a small amount even after numerous 

 attempts. The types of bottom which gave the greatest difficulty were 

 those which contain stones large enough to become caught in the Jaws 

 and hold them open, and those with a substratum of hard clay. 



In 1928 and part of 1929 the samples were washed through a 

 series of two brass sieves having meshes of 1.0 millimeter and 0.5 

 millimeter. This method was found to be so laborious and time- 

 consuming that it was abandoned for the more efficient method of wash- 

 ing through a dip net with a bag composed of No. 36 grit gauze. By 

 the latter method a sample could be washed over the stern of the boat 

 while it ran between stations. The entire operation consumed only a 

 few minutes, compared with about one hour by the former method. In 

 addition to the saving in time, the delicate bottom organisms suffered 

 less mechanical injury in the net than in the metal sieves. 



The bottom organisms were identified and enumerated in the 

 laboratory. In all but a few cases, all of the organisms in a sample 

 were counted, but at certain stations, such as Stations 200 and 250, 

 the Tubificidae were taken in such large numbers that it was found 



251 



