5. In June: Clicetoceros Villei, Stephanopyxis turgida.
6. From June to November, December: Centropages hamatus, Tintinnopsis he-
roidea var. acuminata, Clicetoceros densus, Lauderia annulata, Rhizosolenia setigera, E.
styliformis.
7. From July, August: Oikople.ura dioica, Proto pedata, Paracalamis parvus,
Tintinnopsis campanula, T. ventricosa, Noctiluca miliaris, Bacteriastrum varians, Chce-
toceros anastomosans, C. coronatus, C. didymus, C. curvisetus, Rhizosolenia deli-
catula.
8. From September: Ptychocylis Claparedii, P. Ehrenhergii.
9. From October, November: Acartia hifilosa, Euterpe acutifrons, Bellerochea mal-
leus, Chcetoceros danicus, C. SchUttii, Lithodesinium undulatum, Rhizosolenia calcar avis,
R. robusta.
All these forms are, with the exception of Phceocystis Pouchetii, of southern habitat.
B. Forms that, as a rule, are confined to the space above the 100 metre plateau.
1. Spring-forms, or such as occur in March:

Southern forms: Northern forms:

Microsetella atlantica, Metridia hibernica,

Oithona similis, Ceratium longipes,

Acanthometron quadrifolium, Chcetoceros borealis,

Halosphcera viridis. v. Brightwellii.
2. Summer-forms, or such as occur in June, July, August:

Southern: Northern:

Evadne spinifera, Evadne Nordmannii,

Ceratium tripos, Acartia longiremis,

C. macroceros. {Metridia hibernica).
3. Autumn-forms, or such as occur in October:

Centropages typicus (southern).
4. Winter-forms, or such as occur in November:

Southern : Northern :

{Acanthometron quadrifolium), {Calanus jinmarchicus),

{Halosphcera viridis), Limacina balea,

Ceratium tripos v. bucephala. Dinophysis acuta.
The parentheses denote that the enclosed species also occur in the spring.
32 p. T. CLEVE. THE PLANKTON OF THE NORTH SEA, THE ENGLISH CHANNEL, AND THE SKAGERAK.
C. Forms that occur in the spring above the 100 metre plateau and In the summer or

autumn above the 50 metre plateau.
1. Occurring in the summer above the 50 metre plateau:

Southern : Northern :

Acartia Clausii, Acartia longiremis,

Oithona similis, Pseudocalanus elongatus,

Sagitta bipunctata. Temora longicornis.
