1911] Michael: Chaetognatha of the San Diego Region. 139 



quency of the species is correlated with salinities between 33.605 

 and 33.648. 



It is possible that the evidence in all the above data may be 

 due merely to insufficient hauling. However, if this is true, it is 

 difficult to see why the data in every case indicate maximum 

 abundance and frequency corresponding to salinities between 

 33.605 and 33.648. This is true whether the data are tabulated 

 with respect to temperature and light or not. Were such results 

 due merely to chance or insufficient hauling we should expect 

 such a variety of tabulation to introduce contradictions, but it 

 does not. Consequently, it seems legitimate to conclude that, 

 other things being equal, jS. bipunctata is most abundant and 

 frequent on the surface when the salinity of the water is between 

 33.605 and 33.648. 



What this relation between salinity and distribution signifies 

 is indeed puzzling. We know that salinity increases, somewhat 

 irregularly, with the depth, and we also know that S. bipunctata 

 is most abundant and frequent during the greater part of day and 

 night in 15-20 fathoms. Are these facts correlated? Unfor- 

 tunately June and July salinities corresponding to this depth 

 have not been determined. We do know, however, that, while 

 the average of the 70 surface salinities considered is 33.641, 31 

 were below 33.605, 14 between 33.605 and 33.648, and 25 above 

 33.648, which means that the salinity most characteristic of the 

 surface is below 33.605. Now in 50 to 75 fathoms, while the 

 average salinity is about 33.964, it is usually below 33.874. It 

 is, therefore, obvious that between the surface and 50 fathoms 

 a depth occurs in which the salinity is normally between 33.605 

 and 33.648. If this depth should prove to be 15-20 fathoms, the 

 meaning of the above data would be much clearer. This specula- 

 tion, however, proves nothing, but it does suggest a possible 

 explanation of the correlation between salinity and distribution. 



SEASONAL VARIATION IN THE DISTRIBUTION OF 

 S. BIPUNCTATA 



In discussing this question it is necessary to confine attention 

 to surface hauls, for our closing nets were not employed suffi- 

 ciently throughout the seasons to warrant adequate interpreta- 



