312 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
PLATE $ 
Upper: Sample dominated by the green algalike plant, Halosphaera viridis, with 
a few peridinians, Ceratium longipes, from a surface haul made off Shel- 
burne, Nova Scotia. X 40. 
LOWER: Sample of midwinter phytoplankton from the inner part of Massachusetts 
Bay, dominated by the disklike diatom, Coscinodiscus, together with a few 
bristled Chaetoceras, peridinians, Ceratiuwm tripos, and a few microcopepods. 
X 40. 
Pate 4 
Upper: Sample of phytoplankton dominated by the oceanic diatom, Chaetoceras 
densum, a surface haul from the west side of the Gulf of Maine. X 150. 
Lower: Sample of phytoplankton dominated by the slender rodlike diatom, 
Rhizosolenia semispina, including one specimen of a horned peridinian. From 
south of Martha’s Vineyard. X 150. 
The diatoms in these two photographs show their specific adaptations for 
flotation, the Rhizosolenia by its slender, rodlike form and oblique ends, the 
Chaetoceras by its development of bristles and the formation of chains. 
(See p. 300.) 
(Both photographs from Bigelow, courtesy U. 8. Fish and Wildlife Service.) 
PLaTe 5 
Urprre: Rather monotonous sample of phytoplankton consisting almost wholly of 
the horned peridinian, Oeratium tripos, with occasional C. fusus, Peridinium, 
and some developmental stages of copepods. Surface haul from off Cape Cod. 
X about 25. 
Lower: Sample of zooplankton dominated by herbivorous copepods, Calanus 
finmarchicus and other species, and euphausid shrimps, Thysanoessa, with 
one glass worm. Taken in vertical haul from 100-0 meters, over the south- 
west slope of Georges Bank. X 4. 
These photographs will give some idea of the relative size of peridinian pastur- 
age and the grazers which feed upon it. 
(Both photographs from Bigelow, courtesy U. S. Fish and Wildlife Service.) 
PLATE 6 
Upper: Sample of zooplankton dominated by the pelagic herbivorous euphausid 
shrimp, Thysanoessa longicaudata, along with the copepod Calanus finmar- 
chicus, two predaceous glass worms, Sagitta elegans, and one naked, shell- 
less pteropod mollusk, Clione limacina, relished by plankton-feeding whales 
when dominating the plankton. From a vertical haul from 100-0 meters off 
Shelburne, Nova Scotia. X 1.75. 
LowEk: Zooplankton dominated by the predaceous glass, or arrow, worm, Sagitta 
elegans, very destructive to copepods and the eggs and larvae of fish. From 
a vertical haul from 80 meters in Massachusetts Bay. X 1.75. 
(Both photograpbs from Bigelow, courtesy U. 8. Fish and Wildlife Service.) 
PLATE 7 
Upper: Sample of an unusually rich catch of haddock eggs, ineluding one of the 
glass worms, Sagitta elegans, known to prey upon them, a single pteropod 
mollusk, Limacina retroversa, and several Calanus and other copepods, 
from a surface haul over the eastern part of Georges Bank. X 4. A single 
female haddock may spawn as many as 100,000 eggs. 
Lower: Sample of rather uniform zooplankton consisting almost wholly of the 
copepod Calanus jfinmarchicus, from a vertical haul from 30-0 meters in 
Massachusetts Bay. X 1.75. (Compare with photograph of same species 
at higher magnification, pl. 9, lower.) 
(Both photographs from Bigelow, courtesy U. 8. Fish and Wildlife Service.) 
