SEA-FISHEKIES LABORATORY. 105 



at the end of 1919, and cannot say that the Noctiluca occurring 

 at Port Erin was part of the swarm that appeared on the 

 North Lancashire coast in December. Ctenophora usually 

 drift about at the surface of the sea in shoals of varying size, 

 and are considered to be more abundant in May, June and July 

 than at any other period of the year.* Pleurobrachia seems 

 to be rarely completely absent from the plankton and small 

 isolated examples are often met with. We have already 

 recorded an extensive shoal visiting the North- West coast 

 of Lancashire in mid June, 1913, which completely filled a 

 tow-net in a few minutes, and numbers were stranded on the 

 shores of Barrow Channel. Pleurobrachia occurred in most 

 of the hauls taken at Port Erin in October and November, 1919. 

 The greatest number captured at one time was 36. Esterly, 

 in an interesting account of the " Ctenophora of the San Diego 

 Region "f finds many more Pleurobrachia in August when the 

 temperature and salinity of the water is highest than in any 

 other month of the year. About 60 per cent, of the collections 

 taken in August contain Pleurobrachia. One collection 

 captured 3,300 specimens and another 1,000. The Pleuro- 

 brachia from the San Diego Region is considered to be a variety 

 of the Atlantic Pleurobrachia pileus, and Esterly states that 

 Bigelow found swarms of Pleurobrachia in the summer with 

 the temperature at 14° and in January when the temperature 

 was 7° in Massachusetts Bay. SteuerJ records Pleurobrachia 

 as being most abundant in the Adriatic from January to April, 

 from 1900 to 1904. From 1898 to 1904 it was of irregular 

 occurrence from June to October and was not taken at all in 

 August. The literature on the subject seems to lead one to 

 the conclusion that these invasions of ctenophora are quite 



1906. Cambridge Natural History. Vol. 1, i>. IIS. 



1914. University of California Publications in Z< 

 pp. 21 38. 



\ 1910. Planktonkunde (Leipzig and Berlin, B. O. Teabner). 



"f 1914. University of California Publications in Zoology, \'<>l. 13, 

 No. 2, pp. 21 38. 



