286 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
curve throughout the year are caused, we find that 
Biddulphia mobiliensis is one of the earliest species to 
appear, and is responsible for the moderate rises im 
February and March. The earhest of the April forms are 
Coscinodiscus radiatus and C. concinnus, which flourish, 
along with Brddulphia mobiliensis, in the middle of April, 
and are followed by Chaetoceros debile at the end of the 
month. In May the great rise to between two and three 
millions is caused by Chaetoceros sociale, and in the early 
part of June by that same species along with Chaetoceros 
teres, C. debile, Rhizosolenia semisprina and Rh. shrubsolei. 
The great elevation at the end of June and beginning of 
July is mainly caused by the same two species of Rhzzo- 
solenia, along with Guinardia flaccida. The rise in the 
middle of October is due to Chactoceros decipiens, and Ch. 
criophilum; and after that period no species is specially 
abundant durimg the remainder of the year. 
Chaetoceros contortum and Thalassiosira norden- 
skioldiz, which were mainly responsible for the spring 
maximum in 1907, have been less prominent this year, 
the former reaching only to 60,000, on April 23rd, and 
the latter 80,000, on May 20th, as against the millions 
present per haul in the previous year. But perhaps the 
ereatest contrast between the two years in the prevalence 
of Diatoms is seen in September, when in 1907 thirteen 
millions and sixteen millions of one species, Rhezosolenia 
semispina, were taken in two simultaneous hauls of the 
surface nets at Station IIL; at a time and locality when 
in 1908 Diatoms as a whole were few and LAzzosolenia 
semis pina was almost absent, the greatest haul being 8,000 
at Station III on September 15th. 
