k 26() TRANSACTIONS LIVERPOOL BIOLOQICAL SOCIETY. 



unduly low by the vertical nets being averaged along 

 with surface and other quarter-hour horizontal ones. 



Occasionally the vertical nets (especially the Xansen) 

 obtained very large catches, but over the whole they may 

 have depressed the sea-average. 



The great majority of the hauls in the bay were taken 

 along a line crossing from S. to N. starting at the Life- 

 boat slip and ending at Spaldrick Creek, and this was 

 known as line I. ; while a second traverse, line IT, only 

 occasionally made, was further out at the mouth of the 

 bay, opposite the ruined breakwater. 



Looking at the records for line I during April, when 

 the hauls were most frequent, we find on the whole a 

 decrease in Diatoms as the month goes on, associated with 

 a rise in Copepoda. As a general rule we find that hauls 

 rich in Diatoms tend to be poor in Copepoda, and rice 

 versa ; and our records show that the change may take 

 place even within the hours of a day in the shallow water 

 of the bay. For example, consider Form 25, on April 

 13th, when the first pair (a) of hauls (A going North and 

 B returning South) was taken (by Mr. Laurie) in the 

 afternoon, while the second pair (b) was taken (by 

 Professor Herdman) a few hours later in the early 

 evening. Although a is a smaller haul than &, it contains 

 more than three times as many Diatoms and nearly three 

 times as many Copepod Nauplii and later larval stages, 

 but less than half as many adult Copepoda. There had 

 evidently, then, been a sudden decrease in the number of 

 Diatoms (chiefly Chaetoeeros contortion), and a certain 

 amount of increase in the adult Copepods, and also in 

 Sagitta, Crab Zoeas, and Gasteropod larvae. 



On the other hand, we have an exception to the 

 general rule that Diatoms and Copepoda do not abound 

 together, on April 17th, when, compared with April lOlh, 



