1s te eh ON ake 
which are given in the accompanying plates, I am in- 
debted to Herr Conrad Schwager, Assistant in the 
Paleontological Museum at Munich, who, at very short 
notice, kindly undertook the task of drawing and li- 
thographing them. As far as possible the figures 
have been drawn to the same, scale of 20 diameters, 
in order to enable theirhrelative dimensions to be ap- 
preciated. In a few instances, in which a_ larger 
scale has had to be adopted, a representation of the 
object is also given, where practicable, on the same 
scale as the other spicules. In comparing the fig- 
ures given in these plates with those of similar spicules 
which are given in the beautiful illustrations of Prof. 
Zittel’s work on Coeloptychium and in Mr. Carter's fig- 
ures of the spicules from the Haldon Green Sand, it is 
very necessary to bear in mind the different scale to 
which these figures have been drawn. In Professor 
Zittel’s work the detached spicules on the Plates [V-VII 
are represented one hundred times magnified, and thus 
five times larger than in my Plates, and the Haldon 
spicules are drawn to the scale of seventy-five diame- 
ters or three and a half times larger. Bearing this 
fact in mind it will be noticed that most of the spi- 
cules from the Horstead chalk are actually larger than 
those from Germany and the South-West of England. 
I may add that the accuracy of the drawings of the 
Horstead spicules is further assured by their having 
been done by means of the Camera lucida. 
Palaeontological Museum Munich. 
November 1880. 
