1923 ] Esterly: Marine Copepoda at La Jolla 425 



main results may be seen in table 3. Acartia clausi was obtained in 

 largest numbers during March of both years. The season of least 

 abundance or of complete absence extends over several months of each 

 year, always covering July, August, and September. A. tonsa reached 

 its greatest abundance in August of the first year and July of the 

 second. The smallest numbers were obtained in January and February 

 of the first year, and in March and May of the second. 



TABLE 3 



Mean Monthly Abundance. The Two Methods of Handling the Data 

 Were Used and the Results Combined. 

 'I' means first year (1916-1917); 'II 5 means second year (1917-1918). 

 Average number of animals per haul 



Clausi Tonsa Small Calaniris Podoplea 



I II I II I II I II 



September 09 74 114 105 80 1365 1597 



October 3 23 22 (39 26 54 599 756 



November 81 34 61 70 13 51 378 565 



December 49 125 35 91 21 166 248 2190 



January 72 90 14 53 12 75 181 746 



February 95 732 8 46 6 16 536 1259 



March 377 1347 SO 35 50 103 429 2217 



April 54 1025 51 42 38 122 455 2100 



May 33 329 33 28 58 58 242 1065 



June 26 24 28 66 46 7 682 1254 



July 28 82 2295 356 71 1755 3226 



August 21 203 204 167 108 1967 1547 



It is hard to say whether the fluctuations from month to month are 

 significant, but there can be no doubt of the general fact that one 

 of the species of Acartia is found in greatest numbers at the season 

 when the other species is least abundant. 



There is a good deal of irregularity in the monthly abundance of 

 the small calanids, and the results obtained during the two years do 

 not correspond so closely as they do with Acartia. During the first 

 year the small calanids showed a well marked maximum in July and a 

 minimum in February. There were two maxima in the second year, 

 in December and April, with the minimum in June. In considering 

 the reasons for these irregularities, we should not forget the possi- 

 bility that the composition of this mixed group of copepods may have 

 been relatively different in the two years. At least there is nothing 

 to indicate that the differences between the two years may not be due 

 to the occurrence of different genera. It would hardly be expected 

 that the seasonal distribution would show such variabilitv if the 



