112 BULLETIN OF THE BUREAU OF FISHERIES 
Pa gi tmociget ahs nly 
& 
Bret ath te Sala tay nt 
SE Hs 
VoAo 
-E 
Ae : = 
HEH 
gestae 
iaspane 
Baa 
Se + ; 7 
VS. 
He: 
Fie. 15.—Occurrence of Rhizosolenia in surface 
collections from May to December, 1922. 
setigera; , Rk. shrubsolei; —-—--——, R. alata 
genuina; . R. alata gracillima; 009000000, R, 
styliformis; —ccem, R, fereensis 
22 4 8 3 
Vode 
A. pre 
Se 
VoSe 
We 
Fic. 16.—Occurrence of Rhizosolenia in surface collections of 1923. 
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 
summermaximum of thatregion, a summerswarm 
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 theconditions at Trieste are of amore 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 thisform. In 1922 
and 1923 it was particularly abundant (figs. 15 
June 
Jule 
Auge 
Sepe 
Octe 
Nove 
Dece 
, Rhizosolenia semispind; -s-smc-e-e, Fe. setigera; 
———, F, shrubsolei; mom, FR, alata genuina; 000000, R, styliformis; tt++++++, R. calcar avis; mmeemm, Fe. delicatula 
