PERIODICITY OF THE PHYTOPLANKTON OF SOME BRITISH LAKES. 39 
were abundant. Spondylosium planum was also very common, occurring in 
short filaments of from 3 to 22 cells. Rhizosolenia morsa was still common, 
and Lyngbya limnetica and Chroocoecus minimus had greatly increased in 
amount. Rotifers fairly common, and а few Copepods. 
Oct. 13th, 1908. Temp. of water 50? F. (=10° C.). Not much different 
from preceding month. А Desmid-plankton of small species, with a con- 
siderable quantity of Ceratium Hirundinella. Ihizosolenia morsa and Lyngbya 
limnetica both common. Rotifers fairly common. 
Мог. 2nd, 1908. Temp. of water 47? Е. (— 8:3? C.). Small Desmids still 
common, but Ceratium Hirundinella greatly diminished in numbers. Ahizo- 
solent morsa at its maximum abundance, and Lyngbya limnetica still fairly 
common. Few Rotifers. 
Dee. 11th, 1908. Temp. of water 46° F. (— 77? C.). The small Desmids 
less numerous, the reduction in the numbers of Arthrodesmus crassus being 
especially noticeable. hizosolenta morsa still very common, but Lyngbya 
limnetica much reduced in amount. No Peridinieæ were observed. Rotifers 
fairly numerous. 
Jan. 8th, 1909. Temp. of water 38° Е. (=8:3° €C.). Great reduction in 
the numbers of Desmids, although Spondylosium planum, Arthrodesmus crassus, 
A. triangularis var. subtriangularis, and Staurastrum jaculiferum (Ё. biradiata) 
are still evident. Much detritus present. hizosolenia morsa reduced in 
numbers, but Lyngbya limnetica much as in December. First appearance of 
Peridinium Willei. Rotifers rather rare. 
Feb. 6th, 1909. Temp. of water 42° F. (=55° С.). The collection 
contained comparatively little phytoplankton. Some of the small spiny 
Desmids were not uncommon, and Spondylosium planum was not infrequent. 
Diatoms were few in numbers and Rotifers rare. The great bulk of the 
plankton consisted of Copepods. 
March 3rd, 1909. Temp. of water 39° Е. (=4° C.). There was a notable 
increase in the phytoplankton. The spiny Desmids again common, and 
Arthrodesmus crassus has reappeared. Spondylosium planum once more 
common. Dictyospherium pulchellum and the young stages of Sphæerocystis 
Schroeter’ both very frequent. A noteworthy feature was the reappearance 
in quantity of Rhizosolenia morsa with rather shorter spines. Rotifers few, 
but Nauplii very numerous. 
April 3rd, 1909. Temp. of water 42° F. (=5'5° C.). A poor plankton 
collection. The phytoplankton consisted mostly of a very even mixture of 
a few species, amongst which the spiny Desmids were the most conspicuous. 
Very few Rotifers or Copepods. 
May 3rd, 1909. Temp. of water 50? Е. (=10° C.). Smaller species of 
Desmids very numerous again, and owing to the relatively rapid divisions 
many abnormalities were noticed among the spiny species. — Spherocystis 
Schroeteri was common. | Copepods and Nauplii both abundant. 
