THE MICROPLANKTON OF PLYMOUTH SOUND. Ay (al! 
disappear at the end. Limacina balea tf. retroversa was common once 
in the middle of the month. 
Chief forms---Asterionella japonica, Chetoceras constrictum, Rhizo- 
solenia Stolterfothii, Skeletonema costatum, Prorocentrum micans, Phia- 
lidium hemisphericum, Obelia sp., Sagitta bipunctata, Calanus finmarchicus, 
Pseudocalanus elongatus, Acartia Clausii, Centropages typicus, Brachyura 
zoeee and Hippolyte larve. 
October. 
S.E. winds prevalent. Chiefly fine weather. Asterionella common 
until the middle, then dwindles and disappears. Biddulphia species not 
yet common. Chetoceras species common at the beginning and fall off 
in numbers towards the end, Lithodesmium undulatum common until 
the middle, Mastigloia sp. very abundant from the middle to the end of 
the month. 
Nitzschia closterium common. Paralia on the increase. Rhizosolenia 
Stolterfothi common at the begining but absent at the end, Shkeletonema 
common and Streptotheca thamensis present with it nearly all the month. 
Of the Peridiniales Ceratiwm bucephalum is fairly common, C. fusus 
present in small numbers, Prorocentrum micans continually present, 
Peridinium divergens sometimes fairly common. 
Laboea species still present in small numbers, and Tintinnopsis ventricosa, 
Pontosphera more frequent, very common at the end of the month. Of 
the Coelenterates Stomotoca dinema and Turris pileata occur although 
only Phialidium hemisphericum and Turris pileata are common. Besides 
Pleurobrachia which is sometimes common, Beroée and Bolina both eceur. 
Annelid larvee rare. Sagitta very common, Cyphonautes continues but 1s 
rare. 
Of the copepods Calanus is still common, but Pseudocalanus, Temora 
and Acartia are the commonest ; Coryceus is also very common and seems 
to follow Pseudocalanus closely in numbers, Centropages typicus and 
hamatus fall oft in numbers. All the larval Crustacea are much less 
numerous. 
Chief forms---Asterionella japonica, Chetoceras constrictum, convolutum 
and densum at the beginning, Mastigloia sp. from the middle of the 
month, Nitzschia closterium, Skeletonema costatum, Ceratium bucephalum, 
Prorocentrum nvicans, Phialidium hemisphericum, Obelia sp., Sagita 
bipunctata, Calanus finmarchicus, Temora longicornis, Pseudocalanus 
elongatus, Coryceus anglicus and Acartia Clausii. 
