112 
BULLETIN OF THE BUREAU OF FISHEEIES 
Fig. 15. — Occurrence of Rhizosolenia in surface 
collections from May to December, 1922. 
— . — , Mhizosolenia semispina: E. 
setigera; , H. shrubsolei: , E. alata 
genuina: ^.B. alata gTaciUivta; ooooooooo, iJ. 
styliforviis; — E. fxrceensis 
starts usually in November and continues until 
March, reaching a maximum in December. This 
compares very closely with the maxima found year 
after year at Trieste. Corresponding to the short 
summer maximum of that region, a summer swarm 
occurs also at Woods Hole, starting usually in 
July and remaining until September. A compari- 
son of the seasonal distribution and breeding sea- 
sons of the zooplankton of the two regions shows 
that the conditions at Trieste are of a more south- 
erly nature than in this region, although it is 
farther north. Its relation to the Mediterranean 
makes the reason for this obvious. The summer 
maximum is very variable, because the local 
neritic species play a minor part, the greater 
part consisting of a single oceanic form (Rhizo- 
solenia semispina). Obviously, conditions be- 
yond the limits of the adjacent coast have much 
to do with the appearance of this form. In 1922 
and 1923 it was particularly abundant (figs. 15 
V.3. 
If* 
Pig. 16.- 
-Occurrence of Rhizosolenia in surface collections of 1923. , Ehizosolenia semispina; 
, E. shrubsolei; ^.i— , E, alata genuina; ooooooo, R, styliformis; ++++++++, E. calcar avis; — 
E. setigera: 
., E. delicatula 
