374 PROF. EHRENBERG ON ANIMALS OF THE CHALK 
are the remarkably formed Actinocyclus senarius, Dictyocha Fibula, 
Dict. Speculum, and Triceratium Favus. 
The other forms represent but a small part of the riches of the 
pail of sea-water collected at Cuxhaven, in which the above also oc- 
curred. 
Fig. 1. Actinocyclus senarius. The fossil shells from Oran were repre- 
sented already in 1837, in my work on Infusoria, pl. xxi. fig. 6: 
here the living animal is figured. 
a. View of the narrow ventral surface. 
6. The same animal from the broad lateral surface. 
c. Empty shells of a dead animalcule. 
d. Broad lateral surface of another specimen. 
e. The same half reverted, in which the central diagonal line, which 
has remained somewhat too light, is to be regarded as reflexion of 
light, not as a septum. 
The polypartite ovarium is easily distinguishable from its partly more 
yellow, in part more green colour. In empty shells three spaces 
(fields) appear to be situated alternately deeper. 
Fig. 2. Antinocyclus sedenarius, known only recent from Cuxhaven, 
has 16 rays and as many chambers; but the septa of the chambers 
form as many again, therefore 32 rays. The structure of these forms 
is, as long as they are filled with the living animal, indistinet, but very 
evident in empty shells. At the margin are 16 apertures correspond- 
ing to the septa of the chambers. 
a. Empty shells. 
6. Shell filled with the animal. The ovarium is greenish. The 
organic contents rendered the determination of the number of rays 
and the number of marginal apertures, which appeared to be far 
greater, difficult. 
e. View of the narrow side. 
Fig. 3. Actinocyclus octodenarius, likewise known only recent, with 
18 rays and chambers. 
a. Narrow ventral surface. 
b. Broad lateral surface, with the green-coloured ovarium grouped 
in the circle. 
c. Empty shell of the same. 
Fig. 4. Dictyocha Speculum. Fossil very frequent in the chalk marl 
of Caltanisetta and Oran, and found living near Kiel and Cuxhaven. 
The fossil form, but a thick-celled variety, was figured in my Memoir 
on the Chalk. There are in those marls far more frequent forms 
which perfectly resemble the living here represented. 
a. The animalcule from the broad side, coloured*green from the — 
ovarium with which it is filled after the first observation and draw- 
ing made in Kiel. 
6. The same, from the narrow surface. 
ce, d, e. Three other individuals with emptied ovaria, with larger — 
or smaller, more elongate or rounded central cell, and with longer 
or shorter marginal spines. The forms d and e are perfectly iden- 
tical with the fossil specimens from Sicily, both in size and in form. 
Fig. 5. Navicula (Surirella) Gemma. Compare Section V. This 
form of large Navicula, observed only in the recent state from the 
North Sea, has admitted the following details to be recognised, which 
