138 MARIE V. LEBOUR. 
and Strombidium caudatum, very easily collapse and destroy themselves 
ina moment. Tvarina fusus we find at a larger maximum than at Kiel. 
Most of the new species, both of the Peridiniales and Infusoria found in 
the plankton by Lohmann, are present here if not in such large quantities; 
thus we have Amphidinium crassum, Pouchetia parva, Cochlodinium 
pellucidum, Laboea strobila, and many other species hitherto not known 
from British seas. 
The diatoms, although usually in less numbers than Lohmann’s, are 
in some cases more. Nearly all his diatom numbers are, however, from 
filter examinations, therefore not exactly comparable. One fact which 
is striking is the relative regularity of the yearly curve of certain species, 
instead of their showing a marked seasonal distribution. This we find 
to be the case with Thalassvothrix nitzschioides, which is present at Kiel 
practically all the year round whilst with us it is a pronouncedly winter 
form. The same is true with most of the Coscinodiscus species which 
also are winter forms here. This is perhaps to be explained by Gough’s 
theory of the distribution of neritic diatoms which he found occurred at 
certain definite times only in places near the ocean, but stayed all the 
year round in suitable localities far removed from it. We find much the 
same seasons for the above diatoms at Port Erin as we have at Plymouth 
(see Herdman and Scott, 1908-15). 
For comparison I have taken from Lohmann’s tables certain species 
with their maximum number in 100 litres and put side by side of these 
the Plymouth records of the same species in the same amount calculated 
from the number in 50 cc. The month of maximum is also recorded. 
It will be seen that in most cases his numbers are higher, in a few instances 
much higher, but in three cases the Plymouth numbers are higher. 
Species. Kiel. a po Plymouth. Bs uy 
Paralia suleata . : 77,000 Nov. — 1,000,000 Nov. 
Skeletonema costatum . 778,000,000 June 25,000,000 April 
Guinardia flaccida 360,000 May 20,000 Sept. 
Asterionella . 1,800,000 Dee. 3,260,000 July (japonica) 
Prorocentrum macans 5,100,000 Aug. 128,000 Sept. 
Glenodinium bipes —. 2,100,000 May 12,000 Aug. 
Ceratium fusus . : 300,000 Sept. 12.000 Aug. 
P. armata 
Pouchetia parva. ; 50,000 Sept. 30,000 June 
Tiarina fusus  . 11,000 Oct. 14,000 Aug. 
As will be seen, the maxima here agree in most cases in being in the 
spring or autumn. As has been stated above, however, there are several 
