196 PROF. W. A. HERDMAN ON THE DISTRIBUTION 
PARACALANUS. 
Paracalanus parvus (Claus) is a southern form (fig. 16) which extends to 
the tropics and has a wide distribution. It is present in quantity only during 
autumn and winter in the Irish Sea, being practically absent between 
February and July, and having its maximum in September or October. The 
largest hauls are in autumn, for example, 59,460 on September 7th ; 138,300 
on September 10th; 53,500 on September 15th, all in 1914; 61,930 on 
August 24th, 1911; 49,800 on September 8th, 1910; 49,390 on September 
Tth, 1912 ; 44,060 on October 24th, 1912 ; while other large hauls in the 
same months range from 25,000 to 40,000. 
Fie. 16.— Paracalanus parvus, from a photo-micrograph by A. Scott. 
This is a species that has varied considerably in quantity from year to 
year, its average per haul ranging from 325 in 1907 to 5863 in 1914. In 
the present year, 1917, it was especially abundant at Port Erin in September, 
along with Oithona. 
OITHONA. 
Oithona helgolandica (=O. similis), Claus, is the most generally abundant 
Copepod throughout the year in the Irish Sea ; but the months when it is 
taken in greatest numbers are June to November (inclusive) with the 
maximum generally in July. There may, however, be a second maximum 
later, in October or November. 
The following may be quoted as exceptionally large hauls :—The highest, 
225,450, is on July 18th, 1911, and the next highest, 199,300, is on 
November 9th, 1914 ; then we have 93,580 on July 28th, 1913, 87,530 on 
September 26th, 1912, and 83,550 on June 14th, 1910. We have twenty 
other records of over 44,000 each scattered over the months June to 
November. This is the Copepod which has the highest average number per 
