124 University of California Puhlicatioris in Zoology [Vol. 13 



by another person and there is some confusion in the data. In dealing 

 with the surface collections for which the salinity is known no hauls 

 have been used for which the salinity given is over 33.85, because of 

 the likelihood of evaporation having taken place. In cases where the 

 salinity is given for the beginning and the end of the haul, the average 

 of the two values is used when the difference is 0.10 or less ; when it 

 is more than this the lower of the two values is taken. The reason 

 for this procedure may be stated as follows : The accidental errors 

 in determining salinities will not exceed 0.10 as a difference betw^een 

 two values for the same sample. While it is known that evaporation 

 has occurred many times, it is assumed that the amount of evapor- 

 ation may be neglected unless the salinity is very high indeed. There- 

 fore, if two values differ by 0.10 or less, the correct value lies some- 

 where between them. Even if one sample has evaporated, the average 

 of the two would be fairly close to the actual value. If, however, the 

 difference between two values is more than 0.10 it seems plain that 

 something more than accidental error is involved. The more probable 

 effect in such cases is that of evaporation, and the lower value is then 

 nearer the true average. If both samples have evaporated, it is still 

 true that the average between the values, when the difference is not 

 over 0.10, gives the more probable salinity. The salinities have been 

 obtained from the manuscript, covering the hydrographic data for 

 all the hauls, that is to be printed in the course of time, and values 

 set down there as determined by the hydrometer and those marked 

 "high" have been omitted. None of the data for hauls have been 

 given here because all the data in the possession of the Institution are 

 to be published separately in a subsequent volume of this series. 



The species of schizopods whose distribution is to be studied are: 

 EupJiausia pacifica Plansen, Nyctiphanes simplex Hansen, Thysanoessa 

 gregaria Sars, and Nematoscelis difficilis Hansen. For descriptions of 

 these forms see Esterly (1914a). The first two species are by far 

 the more abundant, but the others are found often enough to at least 

 warrant their inclusion here. 



The hauls considered in this paper extend from June 15, 1908, 

 to April 17, 1913, inclusive, and with the exceptions already noted 

 the hauls in the same month of the different years have been combined 

 in each of the three tables that follow. The animals included in the 

 enumerations are only such as have been certainly identified. "Wliile 

 it is not likely that all are sexually mature, larvae and juvenals about 

 which there is any uncertainty have been excluded. In all, the body 



