186 MARIE V. LEBOUR. 
(21) P. ovatum (Pouchet). Common in late summer but rare in May 
and June. Specimens with broad and conspicuously striated 
interspaces between the plates are as common as the typical 
forms and are probably older, as Mangin (1913) has already noted. 
More common in tow nettings than in water samples. 
(22) P. pedunculatum Schiitt. Very rare, in water samples only. 
(23) P. pallidum Ostf. This and the following species are both 
common, the present species being larger is commoner in the 
tow nettings. 
(24) P. pellucidum (Bergh). Common in water samples. 
Sub-genus EUPERIDINIUM Gran. 
(25) P. oceanicum Vanh. Rare in tow nettings. 
(26) P. divergens Ehrl. Abundant in the tow nettings, especially in 
August and early September. Following Meunier (1910) I have 
reunited the P. depresswin of the ‘“ Nordisches Plankton” with 
this species. 
(27) P. crassipes Kofoid. Not very common in the tow nettings in 
August and September. 
(28) P. conicum (Gran). This species and P. divergens are almost the 
only peridinians to be found in winter: although not abundant 
P. conicum is found throughout the year both in tow nettings 
and water samples. Commonest in early spring. 
(29) N.R. P. Thorianum Paulsen. Rare in water samples in June. 
Meunier (1910) gives good figures of this species, which resemble 
the Plymouth form more than do Paulsen’s. The present speci- 
mens have small knobs conspicuously ornamenting the skeleton 
which are very characteristic. 
Genus PYROPHACUS. 
(30) N.R. Pyrophacus horologicum Stein. Occurred very rarely in tow 
nettings in August. 
Genus OxytToxum Stein. 
(31) N.R. Oxytoxum Milnert Murr. and Whitt. I have referred to this 
species, a very small Oxytoxum about half the size of the type 
but agreeing with it in form. Only one specimen was found in 
August in the water samples. 
